National Instruemnts does not make a PXI or cPCI card that acts as a USB carrier, so I hunted one down online. Here is the link to the site I found:
http://www.ekf.de/c/cusb/cb1/cb1_e.html#PI
We have never tried this card, but it looks like it should suit your purposes fine.
Ryan Tamblin
Applications Engineer
National Instruments