I suck when it comes to car modifications and was wondering (and hoping) someone near me can assist me. I'll come to you, and bring the stuff needed PLUS a six pack!
Which switch do you want to use? If it's the Radio Shack version (or something similar), my installation, based on Evan Fusco instructions, is documented here. I consider myself somewhat mechanically challenged as well, but it was a fairly simple process. I suspect I'm further away than you're wanting to go for assistance, but I'll be glad to help if you don't mind a five-hour drive.
It's really not tough, and I promise you it's a rewarding experience when complete. My instructions are very detailed and I've never had a report of a complication. Read them through and see if you think you can do it. If you're still not comfortable with the DIY, check with a local car radio installer (I'd pick a small/private shop) and see if they'll do it or help you do it. I've heard price ranges of $25-50 quoted to others. The benefit there is that they're very comfortable with the dash pieces and snaking wires where they're supposed to go and such. If you provide the instructions and parts and are flexible with when to get it done I'm sure someone could help you.
I did...but somehow I read it as Hobbit, not efusco. My apologies, I seem to be getting dyslexic or something in my old age.
The said instruction http://www.calcars.org/prius-evbutton-install.pdf is for 2004. Would it be the same for 2009? Thanks!