For those that have multiple external HDDs connected to your PS3 and are using the gameData.pkg (released a few weeks ago) this tool (tweak) may be helpful to you, so you don't have to be swapping USBs in order for the gameDATA app to see your current external HDD as the (1) main ext HDD. So for those that have been enjoying the latest PSN DUPLEX backup games, but running out of internal HDD space, plus those that have more than one external HDD (and don't wish to be swapping the external HDDs so they can be identified as the (1) USB drive, this will help you.

You will need:
multiMAN- Download
gameDATA.pkg- Download

know how to use multiMAN's file manager or using FTP to transfer a folder.
more than one external HDD--if you have only one external HDD--they you don't need to bother using this--unless you tend to use a USB stick every now and then to install small files to your PS3.

Installation Instructions

Source- psx-scene