The compressed air sounds like the way to go if you have the tools.
If not, have you tried using something very sticky, like gorilla duct tape twisted firmly to your ram-rod with a balled up wad (sticky side out) on the end? You should be able to pin the powerbelt to the bottom of the barrel, stick to it, and pull it out.
If you are able to pin it to the bottom, but even the gorilla tape isn't sticky enough, you could apply a small dab of 5 minute epoxy to that wad of tape and then pin the belt. Let it cure for 5 minutes and then pull it out. The downside to this is the possibility of getting a little of the epoxy in the flash-hole or on the lands (although the powder would keep it out of the flash hole I think). In any case, it would be easy enough to clean out with a strong solvent because that type of epoxy doesn't fully cure for an hour, but just be aware. It would only take a VERY small amount of 5-minute epoxy if you are indeed able to pin the plastic power belt down at the bottom. Just enough to cover that wad of tape at the end of your rod. Then let it cure half way (2.5 minutes) before going in so there is no possibility of any dripping off. Try the duct tape method first and see if you can even pin the sucker down flush.