This can be done by using SVN externals:
This will allow you to create a subfolder in your current directory that contains a reference to another SVN repository. You may also choose the specific revision when creating the SVN external.
After creating this subfolder, you can create a project reference to the project inside the created sublfolder.
Alternatively, you may check out the specific revision of the project to-be-referenced, then create a project reference to the checked out copy.
