To quote: Due to FAT32 limitations users needed to run these games from internal hard drive only. However, it seems that isn't the only option anymore. Many games utilize a file format known as PSARC (*.psarc).
These files ending in .psarc are archive files similar to zip or rar files on PC. By extracting these large archive files and using the smaller files that are inside, users can get stay under the 4GB limit.
This method has been tested on Uncharted II, and will only work on games utilizing the psarc file format.