http://www.doxbay.com/usb-flash/
How can I combine 2 USB flash drives, no hub?
I wondered if you could combine 2 flash units to fit a single port. I tried to make the best use of limited ReadyBoost with a USB Flash Drive to run from RAM.
Get a big flash will more, if supported. There are no good form of "combine" two units to have one. Technically you can do this with RAID hard drives, but I do not think it will work with USB, and do not think you wants something from this complex.
How to mod a USB Flash Drive