I just got an email from Ascent, and they now have the SDK for fit format, and they are working on getting this working. They have Garmin 500's, so they are eager to get it working. You'll find the same problem with ridewithgps. You would think they would release the SDK to application developers before they release it to the public ... oh well.
You can always export as tcx file, then import into Ascent as tcx.