Net 4.0 Wpf UserControl Library- Can it be referenced in a VS 2008 Package ToolWindow

Question

I have a project to build an Extensibility Package with a toolwindow using a WPF UserControl Library. I have VS 2008 and VS 2010 versions. Reusing the Wpf for both versions is easy to do if I keep the Net framework to 3.5 or less. There is an existing Silverlight 4.0/Net 4.0 application that I have been asked to convert to the WPF. It uses a lot of the 4.0 features and reworking it to a less version is major work. I have run tests to try using Net 4.0 Wpf and the VS 2008 Package refuses to recognize the reference.

My question is this: Is using Wpf Net 4.0 in a VS 2008 Package doable in any way?

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Answer 1

The answer from the VisualStudio Team is- No, no hacks, no round about, no way