If you can swing a few more than 7 days, in 2011 we did a nice loop out of Missoula. Followed the TransAm route for a few days then went over the Pioneer Mountains Scenic Byway to Wise River and Divide, thence to Twin Bridges, where there is a very nice bike-only camping facility. From there it was on to Butte and then Philipsburg, which is very cute. From there, there are a couple of options to get back to Missoula. Only catch is that there is a 20 mile stretch of unpaved road between Melrose and Twin Bridges that is somewhat rugged in a few places, but we managed easily on our LHTs. Worth the extra effort, IMO.
There is also the loop out of Whitefish that goes into B.C. and Alberta and then back into Montana and over Going to the Sun Road in Glacier National Park.
Send me a PM if you would like details.