Having been reminded by kaputnik of this, here is a possible route with markers of interest:
http://www.mapmyride.com/routes/view/71819692
Please feel free to add or comment. There are possible extensions - e.g. over the Meldons and back via Romanno Bridge (that's quite a big extension) or to include West Linton. I have indicated some possible food stops: near Eddleston, Whitemuir, Carlops. On this route we might see moorland wildlife and we would also pass by Gladhouse Rsr.
I suggest we start from Eskank (why would I do that :) ) by the two (formerly three) craws.