Adding items as links is not supported yet, but is high on our todo list for Visual Studio.
Unfortunately it is not supported in the MPF framework (Managed Project Framework) from Microsoft that we have build our project system on.
It is supported in the new 'Common Project System', but that has other flaws, such as no support for the Windows Forms designer.
For now we have decided to build on top of MPF, which means that we have to add features such as this one, and also the feature to 'Show All Files' and Include/Exclude files.
We hope to have support for this in the next build or the build after that.
XSharp Development Team
XSharp Beta 8
"We have implemented “Linked Files” in a project. This is useful for example if you have files with common code that you want to include in different projects, like global attributes with company name, product name etc."