Is it possible to reduce game size?

I want to download gta IV and play it on my ps3, however my usb has a maximum storage capability of 16 gb(gta is 18gb) :/. So as the title says, is it possible to somehow make the game smaller? So that It can fit on my usb :D? If not I'll probably buy an external harddrive(probably was going to end up doing that anyway).
Many thanks
Liam