You could get some really nice singletrack in the Leanachan Forest on the way out of Fort William. There is a big network of trails based around the Aonach Mor car park. Then there are a few paths marked on the maps between there and Laggan where the next interesting section could start but I've never ridden them so can't comment!
If you are willing to add some distance you could go a round about way, through the head of Glen Nevis along the boggy as hell path to Corrour Station you can find some nice descents down to Loch Laggan after riding along beside Loch Ossian and from there to the interesting bits at the Wolftrax or at the end of the EHW!
Either way the scenery will be good as long as you can see the hills through the clouds/midges
