Well there are two types of AGA games, the first type
is the ones that basically use lower level stuff like copper
lists and what-not or the blitter directly and the second type
goes through system library routines.
The first type will be a nightmare to produce some kind of
abstraction layer for - therefore it will never be done. Use UAE.
The second type can sometimes be made to work through
mode promotion software, which you can look for
on aminet. No gaurantees though.