I have done a few routes – nearly all landrover track tho but all weather
The train is not a huge help. You could get the train to longniddry and take teh old railway to haddington then south on road to gifford. Or just ride out on the pencaitland railway walk . One climb I have done is by stobsheil farm a bit east of Humbie, the other from longyester over lammer law. should be able to make a circuit there somewhere.
Edit – I think thats pretty much what Druidh posted 🙂
There is a nice scenic but not hugely challenging circuit – out on the pencaitland railway to just beyond ormiston, left turn on a branch towards new winton and pick up some paths thry u the woods, down thur butterdean wood towards haddington, old railway to longniddry.