There's a much easier way involving not 2, but 1 memory stick, making the swap trick useless for now, I guess.
Instead of making the same directory on both memory sticks, make 2 directories on the same memory stick, but make one ending with %
So if you have a directory called "DOOM-PSP", make another called "DOOM-PSP%" and put all your files in the directory without %.
Source:
http://www.pspjunkies.com/content/view/443/1/
Edit: Apparently, you need a software to be able to do this. Go to the site mentioned above for more information
This update also does not seem to work on versions
1.51 or
1.52 of PSP firmware.