I've know about parties with a mandatory 'fit' body requirement, but nothing in my area.  I'm willing to travel for a good party as well, but still nothing within 120 miles of here is for humans only.  I suppose one way of separating the healthy from the fat would be to host a party at the end of a long hiking trail, or on top of a mountain somewhere.  The fatties would fall by the wayside while the humans would just leap over their bodies as they came rolling down the slope.