I think I see what you mean (A VS 'Add-in' is a plugin for Visual Studio, right?).

It seems like you have two choices then:

1) Create a VS add-in project, add the build rules for each ui/mocable file manually (as you say, not very practical, but not too much trouble if you only have a few files that need it).
2) Create a Qt project and see how it differs to an Add-in project. Then canibalize the bits from the Add-in project that you need to turn the Qt project into an Add-in project.

I no longer work on the Windows platform, so I don't have VS in order to see how to do this. Maybe someone else can help. Try experimenting in the meantime.