I have successfully overcome wear on the early ProConnect frame with the stainless steel
Surly Hurdy Gurdy chain tensioner. This works well with the forward facing drop out BUT sadly does not come with the necessary flat to act as the non-rotation washer on the chain side of a Nexus hub.
In my case, using a Rohloff hub, the Hurdy Gurdy is on the chain side and a long/substantial torque arm prevents rotation on the non-chain side.
Typically the Nexus hub will be using the Black/Silver pair of Shimano non-rotation washers with forward facing dropouts; one on each side of the frame. It may be sufficient to use only the one on the non-chain side.
The insert washer supplied with the Hurdy Gurdy is only appropriate to wheels secured with quick release spindles.