Not been right through, but I approached from the north. From the south also seems pretty standard by bike:
http://www.walkhighlands.co.uk/Forum/viewtopic.php?f=9&t=6103Looks like a couple of miles of single-track through the pass to link up vehicle tracks - I think it would be fine though (been meaning to try it mysels but not got around to it).
You'd be lucky to get the bike up Leathad an Tobhain from that direction - thick heather and peat, path is barely visible until you get higher up onto the plateau. There is a good track up to Meall an Uilt Creagaich further east that can be cycled, but you'd need to do some heather bashing to get onto that from the Tromie (I think there are more vehicle tracks than the map shows, but they don't link up and I can't remember the exact extent). You'd be best starting from the Feshie for that.
Here is another good bike/hike in the area:
http://www.walkhighlands.co.uk/Forum/viewtopic.php?f=9&t=4514