Yup, that's the one. Only needs about a 1/2" hole to poke around.
As much as I hesitated, it turned out to be easiest to find inconspicuous places to cut one or two gang holes that I later covered with blanks. Someday I'll have them closed up properly.
For as much as I avoided making any holes, my home builder was doing work and cut holes all over my house in like 5 different rooms to do moisture testing... Took their guy about a day to patch, texture and paint everything and you'd never know today. I kept his number! People go to such extremes to avoid cutting and patching but honestly it's generally faster to cut any holes you might need, run wires, then patch & paint.
You should learn the drywall patch technique. I have developed a way to do it combining several tricks I found watching this old house, the internet, and other random shows.
1) Measure and mark out around your hole and cut back so that it is a nice and pure rectangle. Razor knife usually is best by drywall saw sometimes is better. If the hole isn't more than 6 inches in any dimension, no need to support it. If it is quite large you can take some scraps of wood and run a couple of them across the opening using drywall screws to hold it to the wall at the edges.
2) Score and snap a piece of drywall that is 1.5 inches bigger than your hole in both dimensions.
3) On the back of that rectangle, measure and mark a rectangle about 1/4 in smaller than the hole in the wall (slightly more than 3/4 in margin around the edge)
4) Score along those lines, snap the drywall and then peel the 3/4 strips off of the paper on the face side. So now you have a piece of drywall that fits into the hole with an extra 3/4 in of paper hanging around the edges. This will serve as your joint tape. It works better than tape because it is firmly attached to your patch piece preventing from falling back into the wall. It also means not dealing with another edge to feather and seeing a raised area when the wall is viewed tangentially.
5) Mark the wall around your hole slightly more than 3/4 in margins. Cut the paper with a razor knife and peel away the paper on the wall leaving the gypsum. This allows you to counter sink the paper from the patch, again, keeping edge feathering to a minimum and preventing the "hump" in the wall that you might see if viewed tangentially.
6) Butter up the back of the paper and along the edges of the patch piece.
7) Stuff it in the hole and use your drywall spatula to set in the patch forcing the extra joint compound out the sides. This step doesn't need to be perfect, but you want to make sure everything is flush or slightly below the plain of the wall had it never been damaged. Always use your spatula moving from the center outward or you may wrinkle up the paper.
8) Let it dry overnight
9) Take a wet sponge and knock off any high spots.
10) Put a second coat of joint compound feather out 6 or 8 inches around the periphery.
11) Let it dry an hour or so
12) Damp sponge it to perfection completely removing any joint compound that got feathered out beyond what was really necessary
13) Let it dry an hour or so
14) Mask off the area so you don't make a mess. Leave several inches of "normal" wall exposed around the area that needs texture.
15) Spray on your texture. Practice first in the back yard.
16) Let it dry an hour or so.
17) Use a mini roller to roll you paint on.
18) Let it dry an hour or two
19) Roll on a second coat this time feather the paint with an almost dry roller a couple feet out from the edges.
20) Done.
The first time you do do this it will take a little while. Once you have done it a few times, you will find that it takes almost no time becuase you will just need a few minutes for each step so it won't really seem like it is taking up any time at all. I have one box in my garage that is dedicated to this. Everything is in that box so I just take it to the work site. Literally, it can take longer hunting down all the stuff than it takes to actually do it if you don't keep a nice "kit" at hand.
NOTE: If you use the joint compound that has a hardener in it, rather than the water soluable type, you can do this whole thing from beginning to end in a half hour. But it is unforgiving to the not so talented featherer.
. Seems like my best bet is still to follow the return air duct. After taking measurements of the softit area in the ceiling it seems like there should be a good bit of empty space. So then the only issue would be pulling wire through the conduit with two 90degree bends in it. I would use smooth rigid conduit and lube the wire so maybe that would make it somewhat easier. 
