place in the main directory of your USB a pkg (it can handle up to 100 pkgs, and the max size for each of them is 4GB). then plug in the usb on the ps3 and run the app.
it will search the usb from /dev_usb000 to /dev_usb009, once found it will start it copy and create the right files to allows you to install it from the XMB without the option. it will also search in the /dev_hdd0/package folder
THIS APP WILL RESTART THE PS3 ONCE FINISHED.