OK ready you have access from above so it should not be to bad. Goto
http://www.lsdinc.com/content/product_details/52 checkout the metal tip push rods. I have been using these for years. Now to try to make this easy with out righting a book,
Shine a bright light into the switch box and go in the attic and look at the top plate you will be able to see the light clear as day ware the sheet rock and the top plate meets. drill a 3/4 hole and push the push rod down the wall right into the back Ko of the box. I use to do this by myself a lot. I taught this to our apprentice a few weeks ago and he has less than 4 month in the field and last week he snaked into a switch box twice by himself. No help from the mechanic. When I asked why he didn't get help from my mechanic he said, "I went up set everything up and I look and there it was so I drilled, sent down, tied on, went down, & pulled the push rod right in and I was done'' it took him 30 minutes total 2 tails snaked down but 9' ceiling.
That brings me to part 2 you might have a problem. On 10' walls they put cats in the bays if that is the case, same steps as above, but you need a 5' drill bit to drill straight down through the cat so use a 7/8 spade to go through the top plate then switch to the 3/4''x5' to go through the plate.
Part 3 grab a hacksaw blade and cut the nails in the single gang box and carefully drop the box into the wall snake wire down the wall and grab it. then use one of the Arlington screw in boxes and done Good luck if you need more help send me a email and I will call you.