Considering that 90% of rabbit pellets are held together by Molasses, and given a recent study that I've read, I know that molasses isn't harmful, in small quantities. BUT They already get enough if they are eating pellets regularly, so I wouldn't suggest adding more molasses to the diet.
As far as digging, Sasami is correct -- it's a natural habit (they burrow all the time in the wild). While you can't make a rabbit completely stop this habit, you can discourage it. Rabbits are very trainable. It just takes a bit of know-how. First, when your rabbit does something you don't want him to do, get his attention. In the wild, rabbits get the attention of other rabbits by thumping the ground. Ground thumping essential says "Hey, look out" or "Hey, listen up!". So, thump the ground (or the bed) when your bunny starts to dig. That will get his attention.
Secondly, mother rabbits (and in other scenarios as well) will growl or make a low, deep noise in their throats to warn of danger/bad behaviour. So, make a low noise, once you've got your bunny's attention.
Do this whenever he does something you don't like, and he will hopefully get the idea.