Well, you can. At least, you can if you are running a gigabye ep43-ud3l mobo. I posted a thread on here previously about having touble flashing. After trying multilbe methods, I finall took a leap of faith. I grabbed my psp, formatted the mem stick to fat32, loaded the psp with the bios update ONLY, and updated in q-flash. Please note that I do have custom firmware installed on my psp, although I dont think that it makes a lick of difference, seeing as you can use the psp as a "removable disc" regardless. I would be curious to know if this can be done on other mobo makes and models as well. Happy flashing!!!!
Most people have at least one RAM/thumb drive laying around and the smallest ones will hold dozens of BIOS versions. If your system will recognize removable drives in BIOS, it'll load BIOS from a thumb drive.
My Epson printer will take a variety of small memory cards and use them as drives to store pictures. I imagine it could be set up to upload BIOS too.
Never seen a psp myself, is the mem stick you mention a thumb drive or a memory card?
Anyway, I'd avoid anything fancy on BIOS updates. KISS is the word.