you only have two options...
either find a machine with a serial port...
or get a usb to serial bridge...
neither of which are 'right now', but they are your only options...
edit: i think you might have a third option too actually, but there are caveats... they are: can you remember the ip address of the inside interface? did you setup either telnet or ssh access? can you actually wipe the config from a virtual terminal session, or does it have to be console access? i can't remember, it's been a while.