Steve, here's a demo of one person's tripod rig where he mounts the preamp under the camera:
https://vimeo.com/34930286
Not sure why your camera would wobble when mourned to the preamp - in my experience they've designed for just that and the camera sits snuggly on top. Maybe a call to the manufacturer is in order to find out why your camera isn't seating correctly?
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Stephanie
http://www.theculinarylife.com