You can't do it because the spec says you can't, basically. It's annoying, but that's the way it is. The CLR supports it with no problem. My guess is that when generics were first being designed, the CLR might not have supported it, so it was prohibited in the language too... and either the C# team didn't get the memo about it then being supported, or it was too late too include it. Delegates are similarly annoying.
As for a workaround... have a look at my Unconstrained Melody project. You could use the same approach yourself. I wrote a blog post at the same time, which goes into more details.
