Thank you for reporting!
Just for the record some ideas, you probably will not consider them but just FYI:
You might get it done cheaper by using cabling from a third party (
http://www.kufatec.de might respond to an email request) and doing install yourself or using someone specializing in retrofits like this.
This guy
craigyb in the UK does a lot of retrofits, he is active in the navplus.us forums and seems to be interested in new kinds of retrofit projects:
http://www.tclsatnav.com
Also a good forum to ask about things like this:
http://www.navplus.us
Also, notes on removing the A pillar, glove box and the roof lighting console are here if you were to go at it by yourself. These are for A6, but A5 is very likely pretty much the same in this:
Bluetooth phone prep and speech dialogue system retrofit Audi A6 (4F/C6) Avant MMI High (possibly relevant also for Q7/A8)
http://www.geocities.com/a6retrofit/articles/a6phoneprep.html
This probably isn't the hardest of retrofits! The trim parts that need removing seem to come off easily (especially if one is not going to remove the front bumper but place the transmitter somewhere else) and cabling is probably limited to power and cabling between buttons and transmitter... of course it will be more difficult if full Audi cabling set is replaced, but if proper retrofit cables are obtained it would probably be relatively easy and similar to hooking up the microphone in the Bluetooth article above.