How to 4 player playing without a multitap

I have a ps2 with a freemcboot installed on my memory card, and i'd like to know if it's possible to have 4 players playing without having a multitap. I have an usb adapter for ps2 joypad that i use to play on the pc but it doesnt work on the ps2. Does someone know if there is any way to do this? thanks

if i'm not mistaken, the game itself has to be coded to be able to use a controller connected to the usb port as an option. the multitap is pretty cheap nowadays, as are the ps2 controllers.... might be your only > 2 player option