I have done this using Pinnacle Games Profiler. It is awesome.
In fact I took it several steps further, so I now have:
- press Xbox guide button for map
- hold Xbox guide button for quest log
- hold left analogue stick down for quick save (this was one of the only other buttons that is not already mapped by the game, so made use of it!)
Works flawlessly and has improved my experience gaming on PC with an Xbox controller immeasurably.
EDIT - if anyone wants my PGP profile just shout. Although it's pretty simple.
EDIT 2 - profile is uploaded here:
https://mega.co.nz/#!UhZwmaII!cPZrcnfgRcM42bWqAxY-N3YpmpAG21l98r4KeL4vTA4