Go Troppo Mate.
Seriously, go on the sick with stress and screw them for all you can. The boss has been negligent in not noticing the bullying and when it comes to him not wanting to pay you any more you can inform him of the reason for your stress and that the company is at fault.
You could go on a right bender really to make the stress more realistic, sitting outside a pub near work, unkempt and draining jugs would well do your cause some good, if anyone from work turns up then just stand up and pish your pants.