Works on Win7 64bit bottles with minimal issues. (Still 3 star to 4 star instead of 5 star rating in this setup, so it doesn't run as well, just well.)
For 64bit games it seems the optimal bottle to use is the Win7 64bit bottle. This option needs to be added to the crosstie, although the "preferred" platform needs to remain WinXP 32bit due to issues with the internal browser crashing on 64bit bottles. A small script to auto-restart the browser helper executable or convince the browser executable it's running in a WinXP bottle by using compatibility mode functions might be a temporary workaround.
Because of personal health issues (toothache) this month, I'll have to lean on someone else to whip up this workaround.