Lol! I've just seen the pic at Amazon...
I used to have one of these loooong ago, although I do not remember about the secondary plug for the pedals... Are you sure it does not go into the wheel directly? I think it does.
Anyway, I believe you're wasting your time with this one... You're going to have to litterally sit on it to hold it. There's no way to hook it to a desk for example, if my memory serves me right. So you won't have a comfortable and efficient position, cause you'll be driving with the wheel just above of your knees.
If you want a cheap wheel I think you'd better get an old force feedback USB wheel than wasting your time with an USB adaptor for the one you currently have. I'm using an MS Sidewinder Forcefeeback wheel and except for a small bug it's working fine. It's over 10 years old now I think, you might be lucky enough to find one for a cheap price. Or something similar. Still you'll need to make sure the drivers exist for your system (the Linux drivers for this wheel have been available for as long as I can remember and they even support force feedback now so all I had to do was to plug it in and calibrate it, but I'm not sure there are recent drivers for that oldie for M$ systems).
Seb.