Some ideas:
Kinlochkeven to Luibelt past Loch Eilde Mor, cross Abhain Rath, back via Gleann Lolorian to Blackwater Reservoir, descend Ciaran Path to KLL. That’s a big ride! If you do it from Glen Coe village then even more so!
Start from Kings House Hotel in Glencoe, head down Loch Etive road. Pick up walkers track on South side of Loch Etive (it’s a bit vague but OK), head up Glen Kinglass to Bridge of Orchy and back to KHH on WHW. Also a big ride.
Drive to Fort William. Get train to Corrour Station (it’s in the middle of no where). Ride back via Loch Trieg, Gleann Lolorian to Blackwater Reservoir, descend Ciaran Path to KLL, back WHH to Fort Bill.