U have used scope rings as flashlight mounts in the past. They didn't put the flashlight on the optimal spot for me, but it worked just fine until I did get a better mount.
You should not need to send it back to Mossberg. Should be able to fix it yourself in a few minutes. Sounds like you have the "feed from the tube" problem. Most common on guns with magazine extensions, but can still happen on all 930's. Just not as common. Brownells has a really good write up...