unfortunately, according to Riverbed, as one of the requirements to "ensure that the WAN optimization solution can be deployed easily and transparently in to the enterprise network", "the solution must NOT use tunnels."
FYI
Technical Requirements for WAN Optimization RFP
http://www.riverbed.com/docs/WhitePaper-Riverbed-TechRequirements-RFP.pdfhope it helps,
bbao