I'd try McFly foam tied in like an egg. You won't see any thread.
Does the client want the fly to float up off the bottom rising above a sinker that rests on the bottom? Some bait fishermen go to great lengths to get their baits a few inches above the bottom, and you can buy floating powerbait. Treated with floatant, McFly foam should float pretty good on the surface, but you'd have to test it for underwater buoyancy. You might have to tie the McFly Foam over a foam core.
http:// http://www.charliesflyboxinc...m?parentID=122