Export as an .obj or .3ds (if possible.) Get Wings if you don't have it already (it's free.) Put Wings in edge mode. Select an edge segment or segments that run vertical between the edge loops that will define the top and bottom of the belt. Hit G and the whole edge ring will be selected. Then go to to face mode and all the faces defining the belt will be selected. Then you should be able to extract and then extrude the region into your belt. If it needs a little adjustment, perhaps selecting the outer rings of the belt and going to vertice mode and using tighten might work nicely. There may be a bit more to it, but that should work. Dunno much about Max, but I'd suppose you could import the model back in. Or perhaps just import the belt back in and fit it to the original model.

---

Barbequed Pixels?

Your friendly neighborhood Wings3D nut.
Also feel free to browse my freebies at ShareCG.
There might be something worth downloading.