I normally try to do the same with my training but the SG that I am training has a tendency to foul out when he starts at PG and only when he starts at PG. A few games he fouled out after like 20-28 minutes and the coach put random players in at PG after that.
I am going to try to go the route of A A B with hopes that players A plays the entire game but if he does get fouled out then player B will be subbed in at PG instead of a random big man.