Go to My Computer, right-click on your flash drive, and choose Properties. Then go to the ReadyBoost tab, and choose Dedicate this device to ReadyBoost.
No. Your USB drive cannot be an extension of your RAM. You can make more SWAP space out of it (or you can store things you don't commonly need on it to have ...
After I waited 2 hours for making an swap file of 5 GB I have disconnected and rebooted the router but my USB was locked to read-only and now I can't use it ...