This question is a follow up to my question about sharing resources between web applications, because I have not yet found a good solution.
I have a web application
One option is to try "Add existing" and in the dialog that appears, the OK button has a drop arrow next to it, change it to Add with a link.
If that doesn't work, rewrite your controls as Custom Controls.
It will take a little while, but will make it much more maintainable in the future.