I think the cone straight up in the air would work just fine, if you are wanting to bend it at a 90 degree angle think of using a 4" pvc pipe fitting sitting on top of your plywood with the cone on the other end.
All entrances will have to blocked closed with the exception of the cone.
I am doing a trap out on a fake stone house right now and used the plywood with cone. Put foam padding between the plywood and the stone to take up the biggest gaps, took some skinny wooden strips (think frame wedges) and drove them in like pegs to fill deep cracks, took silicone caulk and went around the edges of the plywood and foam trying not to get too much on the stone itself, and all was held in place with tapcon screws.
Be sure to anchor the bait hive down with a ratchet strap.
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