As of yet, there is no known patch that exists. The R4 is still lacking support for SDHC. And although using a 4GB micro-SD card is possible, it will be unstable or not work at all.
The R4Ds does not support a 4 gig SDHC theoretically you could use one that not SDHC but i do not know if you can still find one Hope it Helps Shummyr