Bob, yes you can do exactly that with the latest TF (latest needed to upload the map to your Garmin).
There is a bit of a learning curve to getting user maps calibrated, but once you get it, it's pretty easy.
Just want to make sure you found this page:
http://topofusion.com/usermaps.phpIt has the best info on using it. Basically, pan to roughly the area the map is in, load it up, then start calibrating points. First you choose a point on the image (you can still pan and zoom around to find it precisely) then choose a corresponding point in "world space" (using any map type in TF, or using your waypoints you have). Do that twice, or possibly twice if the map needs to be rotated or skewed. Then you should be good to go.
Feel free to ask questions if something isn't clear -- I'm here to help. Though I will be on the bike all day tomorrow.... out GPS'ng and testing the Custom Maps KMZ upload feature...