I would like to be able to accept null/undefined values for CLR methods that accept 'object' for the argument type.

Would you please consider this ability? I have a fork that allows this here:

http://jurascript.codeplex.com/SourceControl/changeset/view/14761#93722

On an unrelated note: I opened an issue on what I think of as a bug for SetMissingPropertyValue here: http://jurassic.codeplex.com/workitem/29997 :)

This is part of the "seamless .NET interop" functionality, which I started working on but never finished.  I'm pretty much exclusively focussed on a different project right now, but some day I'll get the time and motivation required to finish it off...