View the Dropout extension adapter at http://www.ortliebusa.com
allows their racks to be mounted further back on the dropout side

If stock upper strut is insufficient length longer are sold also.

Ditto going with a QR Axle mount
http://www.tubus.com/product.php?xn=33

I'm using the Tubus LoGo, & a Back roller set.. sliding hooks Fwd, shifts Bag Back ..
(though, I'm not on a Surly cross-check)