PS: after looking around a bit, those modular front panels from FrontX don't seem to be so expensive anymore though...
Anyways, when searching I came across this too:
http://cgi.ebay.com/panel-mount-USB-2-0-female-Ma...ash=item35ace1e871
And this looks like it has 4x 1-to-1 USB connection (according to the comments)
http://www.newegg.com/Product/Product.aspx?Item=N...ID=skim1132X509988
Here is a complete DIY guide for the exact thing you want:
http://www.azog.org/?p=152
EDIT: ah, you _don't_ want it on the front of your PC? Oh well.... /me slaps dodgy Sam
Then why not simply connect 6 cables to the back of your PC and strap them together and glue the connectors on top of eachother?
And if you realy want to go fancy, do some shrinking tube around the 6 cables, and a big shrinking tube around glued together connectors....
/ 
