Hi Dan,
At this time, ModelRight doesn't support permissions. We were thinking about that feature more like an administration feature. However, we've had enough request about it that we're thinking of adding it in the near future.
In meantime, you can use Post Scripts. ModelRight allows you to write little VB scripts that get executed whenever an object is generated. Such script can be easily used to generate grant permissions.
Hope this helps.
ModelRight Evangelist