Long time no see (I'll play the level tomorrow, need to zzzzz before work), but FYI you can force a near-infinite amount of boxes into a Sokoban level. (Well, maybe not thousands since it might overflow the game's internal object limits, but you get the idea.) You just need a slightly more complex setup.
You need a texture where floor A and any other floor are
wildly visually different. Think floor A vs floor D in built-in Garden texture, or a custom texture with a similar feature. That's because boxes will be forced to go on floor A, and you will have no other visual indicators.
Next, all destination tiles are covered with OPEN GATES.
(That's why there can't be other visuals, and you do want the player to SEE the destination tiles... "gates are floor A and everything else is floor <X> is the only way)
Then, outside of the level's boundaries, second character is standing on that button. When ALL the boxes are in gates, second character can step over a one-way conveyor belt, closing the gates once and for all. Gates snap shut, boxes are all gone, generator kicks in and presses the one actual button you need to exit. (Optionally, it can also re-press a second copy of the "main" button, so that there's no "stuck on the wrong side of closed gates" issue.)
at least the puzzle bit 
In pure Sokoban clones, inside other games, etc... It's kind of destiny at this point. I think it'd be neat to see it in Wonderland.
