If you don't already own the converter, why don't you just E-mail Andy and see if he will sell you just the USB cable for it.
(I've had bad luck with my QVS PS/2-->USB converter. Works okay for keyboarding (which is what I use it for (with a PS/2 Keywiz), but it would suck if I used the keyboard for gaming). Not sure if the I-PAC would have the same problems.
Another option is to get a six-foot M/M PS/2 extension cable and plug the I-PAC into that and hot-swap it, which is what I do with the KeyWiz.