You can do it by using latest Microsoft Research project [Moles][1] [1]: http://research.microsoft.com/en-us/projects/pex/ OnceMoles
Once you get it running
You, you can do following
MMyProxy.DoWork32 = () => put your mock result here.
MMyProxy.DoWork32 = () => put your mock result here. Remeber SetRemember to set moleBehavior to fall-through for the unmocked methods.