I think you can find creative ways of making that data happen... give me a moment to map it all out.
Edit: Here's the order in which the characters are removed, and readded (but it doesn't included initial introduction).
Stuff in paren are characters you may want back.
+1 Kain
+1 Tellah
+3 Rydia, Rosa, Yang, remove (Edward)
-1 Tellah
-1 Yang
0 remove (Palom), (Porom)
0 remove Tellah
-2 Kain, Rosa
0 remove (Cid)
0 remove (Yang)
+1 Kain
+1 "remove" FuSoYa
-1 Kain
If we're clever and figure out how to modify the shadow RAM, we could simply try to fit in 4 characters out of 5 in FF4A to swap in/out of the party. What would be required though is to not include FuSoYa and create a new copy of him for the Zemus battle.
That would be how it could be done. Edward is probably the best candidate to "kill off" since he's part of the cap casualty. If you can manipulate the latter 4, you can certainly keep them around IMO.