Yes, you can. You need to format your key as a SWAP format and have it inserted
when you boot. Ubuntu detects the SWAP and will use it. More SWAP sometimes
slows your system because RAM is faster than disk caching. It should not exceed
the amount of RAM you have. You can partition the key to create one just the
right size. Use Gparted or Qtparted. In Ubuntu it is found on Syastem,
Adminstration, Partition manager.