He encontrado en GBArl de un modchip del que comentan que tienen estas características, y por 14€:
Internal modification control chip for Nintendo DS
Add two functions to the X and Y buttons when playing GameBoy Advance games
3 modes: Turbo button mode, L/R mode, and OFF
Turbo mode: X and Y function as turbo buttons for A and B
L/R mode: X and Y function as R and L for GBA games
Toggle modes by pressing Select + L
LED indicator for chip functions
Easy to install - 10 wires to solder
Chip comes with stick-on insulation tape and pre-cut soldered wires
Detailed instructions and full diagram available
Lo veis con futuro?...
ModChip