You still have the problem that anything on the load side of the main bonding jumper is a feeder (4 wires) and the bonding jumper needs to be in the service disconnect enclosure.
Tell us more about the transfer equipment. Is it creating a Separately Derived System (switching the neutral).
That still may be where you want to set the service disconnect even if it is on the outside wall. You still have the 4 wire feeder problem tho.
