I just checked the implementation, and EXPORT_PROPERTIES does not support generator expressions for specifying the property names, so that rules out that idea.
EDIT: Although now I’m wondering if the exported case would use the same generated <package>-config.cmake file and would therefore still pick up your set_target_properties() command in there. If it does, then you wouldn’t need EXPORT_PROPERTIES at all. Sorry I can’t be more specific, I pretty much never use the “export-in-place” scenario, so I don’t recall the finer details of what it does under the covers.