best be on a ups if you plan to do that
Why? Until you put any bitcoins into it, the wallet is worthless, so losing it won't be a problem. It's no different from the livecd approach, except that instead of running a whole OS in RAM, you're just storing a folder in RAM.
If you ever need to use the wallet, just keep a copy on whatever medium you used to back it up, and copy it back to your ramdisk. where you make whatever changes you need to make. I don't know if you even need to overwrite the old copy with the changed one, since all the transactions are tracked/confirmed by the network.
Edit: If you thought I was suggesting not to keep a back-up on a physical medium, that is definitely
not what I was saying. It's
always a good idea to keep a back-up. Thought I'd clear that up, just in case.