Linag that's a great question. Obviously no other fruit has that wonderful pineapple flavor. Papaya would be the closest from an enzyme point of view in that it contains a lot of papain, a proteolytic enzyme like bromelain. Maybe adding some green apple will add the texture and tartness you get from pineapple.
I would love to hear what other ideas you smart people have! More heads mean better ideas.
Wally Bishop C.N.C.