also sometimes called an active extender or powered extension cable... they allow up to 30m
Just guessing here, but I think the usb signaling pair is bidirectional of sorts, so something easy like a buffer IC wont work since it's only passing one direction.
maybe something like a 74HC4061 analog switch would work (don't use the switch part, just tie the switch select low so it's locked into one set of outputs) ... setup your D+ and D- on one side of the switch, and the extension of your D+ and D- on the other side ... the bidirectional nature of the analog switch will allow a signal to travel either way, but at the same time, it is buffering(?) the signal as well... maybe?