Install the GBA cia to sysNAND with BigBlueMenu running from Gateway Red Card after booting Gateway into sysNAND mode (hold B and press A at Gateway Menu then press x at the prompt to continue to sysNAND mode with Gateway Rom Menu access). Install FBI cia to sysNAND as well and you can flash patched AGB firmware to NAND with FBI. Then boot into emuNAND and install all GBA cia to emuNAND and they will work from emuNAND. To save a little space, another member of the forums created a
tutorial on making GBA cia forwarders of about 500kb each that can install to emuNAND and launch the GBA game.