Add-in project must be .NET 3.5 rest of the codebase is .NET 4.0 how to solve?

Question

I wrote an add-in for Inventor 2012, the add-in must be .NET 3.5 it seems. I have not found an update that enables .NET 4 yet. The rest of my codebase is .NET 4.0 and hence I cannot reference my other projects from my add-in code. Is there a workaround for this?

Answer 1

No. You could spawn a separate process and talk to it, but other than that, outta luck.

Answer 2

It looks like Inventor 2013 is compiled for .Net 4. That is not a patch I can easily apply at the moment.