I had it working and it is not worth the effort.
To give you an idea of the complexity of the project.
Here is 1/10 of the circuit
All this was so the PSP would see the second stick when the switch was changed
SD1 is memory stick one and SD2 is memory stick two. The other side is where it plugs into the original memory socket.
The circuit all fits inside one chip. A 100,000 transistor CPLD custom gate array.
The chip is not expensive about three dollars.
You have to have a fast pc.
Gate array design software.
Emulation system to test
Jtag device to program the gate array
Soldering skills for a 64 pin surface mount chip
I designed it ran it on a simulator software to make sure it worked and then someone came out with a
SDHC card to pro duo adapter which I got from DealExtreme for $6.50 and another company is releasing
a dual SDHC card to pro duo adapter allowing you to run two 16 gig SDHC cards and no switches.
Your time has to be worth something. If you are doing it to learn something valuable then go ahead.
I am not trying to tell you how to spend your time.
Just saying been there done that and most people have no idea how complex it is.