The front panel connectors on the 1480A are pass-thru so you can connect a single cable to any of the front panel connectors and attach to your bus under test (D+ & D-). Please note that this will create a long stub so it is very important to keep the cable / grabbers between the bus under test and the 1480A absolutely as short as possible. Please also note that, if capturing HS data, the capture must be started in the 1480A before the device under test is connected to the host under test. This is further explained in the below support forum post:

http://www.internationaltestinstruments.com/boards/t/113/the-1480a-capture-must-be-started-before-the-device-under-test-is-connected.aspx

Depending on the exact reflections encountered, you might also try to slightly vary the length of the attached grabber cable. This has effect on reflections and signal integrity.