Randy, it's very common for BSF to mix with worms and I don't think it bothers the worms. They actually do very well on the residue left behind by the BSF.

Rigging a ramp could be fun if you have the time and patience but I think you can round up the mature grubs without one pretty easily. I think you could use the same basic idea as the method I use for harvesting juvenile grubs. Here's the post where I explain that procedure: http://blacksoldierflyblog.com/2008/07/25/collecting-immature-larvae/

The mature grubs don't eat so you would need to attract them into the container with what they want which is a dry protected place to pupate. I would try using a similar container as in my post and I would fill it with shredded paper, dry leaves, sawdust, etc. To maximize the effect I would put the container right up against the inner wall of the bin because when the grubs try migrate out of the unit they circle the perimeter. You might want to find a square container or a round one with straight sides so you can snug it up to the wall. For that reason I would also have some of the holes as close to worm bin wall as possible.

Randy I remember discussing that our fish prefer to eat the juvenile grubs, but I've been having good results using the mature dark grubs as chum. They tend to float for a while and when I fish my pond I just throw out a few handfuls of the dark grubs and it really gets the fish's attention.

I caught another brown bullhead on a BSF grub recently and the brute weighed in at 1lb 15oz. It was fun hauling him in on my 10' brim buster. It was tasty too. \:\) I found some crawdad parts in it's stomach...