Thing is, worms don't really move if there's food where they are even if theres new food elsewhere. So it can take a LONG time for all the worms to move to where you want them. I moved away from bins mainly because of the harvesting reason. BTW everyone has their favorites but I love the Worm Inn. Very breathable, no stacks to move, and the stuff out the bottom is nice and consistant. No wet VC.

But to your harvesting problem, you could try this method.
http://www.youtube.com/user/TheCompostGuy#p/u/25/BhyTzhPtJcg

Add a small layer of VC you want done every couple of days until is all done. One advantage is it's based on running with the new system so you can spead it out for as long as you want.

I'll check out that video tonight. I plan on moving to a flow through system as I have a lot I can put in and the 27 gallon bin is just to large to move around.

I'll probably build one myself, I just need to decide what I want to make it out of a 55 gallon drum or a trash can with wheels. I'm thinking trash can right now just because the wheels will help.

On making one, check out this thread if you hadn't already spotted it.

http://forums.gardenweb.com/forums/load/verm/msg0903044524247.html?8

Once every so often I sprinkle corn meal on the surface of my worm bins. Do it one day then check the bin the next day and you will see that a lot of worms have come to the top , works every time they love it.