For trailer biking, you'll not do much better than the Sustrans route which runs off-road from Killin to Balquhidder then on to Callander. There's a burger/coffee van at the top of Glen Ogle too.
Slightly further afield, there's another nice option round Loch Katrine and you can get the boat one way then cycle back.
There are some easy, waymarked trails on Drummond Hill just opposite Aberfeldy, off the A826 round Loch Kennard and then down and around Dunkeld. From Dunkeld, there are a number of tracks up and around Loch Ordie.
In short - you shouldn't run out of options.....