Un-shielded USB 2.0 Signal Connector
Are you running USB 2.0 at full or high speed?   Is this USB interface internal you your system or does it need to pass USB compliance testing?  

I'm guessing you can't add any gnds to your cable or connector on either side?  If you could that's definitely something to try.

Short of that you could try some series resistors, or series ferrites or even small caps in parallel.  All of that will slow your edge rate down or reduce the amount of high frequency content of your signal.  Of course that will close your eye a bit too and may violate spec. 

Finally maybe a common mode choke like this one made for USB 2.0.   That will take out any common mode component.