Alternative options? How isn't 4MB of RAM your limit? The only other way you'd get extra RAM is from certain slot 2 devices (Opera ramcart, certain flash carts, M3 has a ramcart). But at which point you'd be forcing a user to buy certain hardware to be able to play the game, and that just isn't right.

Pass tasks on to other parts of the hardware? I hate to tell you man, but all you have is the ARM9 and ARM7, and the ARM7 isn't going to do much for you.

You wanted to use MP3's earlier, you obviously don't know what you're at, and your project is nothing more than a sham. Stop fishing and go back to your "speed-painting".