You should make a new user widget that encapsulates the functionality of that button, and just re-use it, put whatever properties you want on the user widget.
That would require some kind of type ducking, mixin crazytown. The WidgetComponent is the UWidgetComponent class, it can’t suddenly expose the properties of the widget it spawns unless we generated some kind of descendant version on the fly that mixes in the exposed public members of the widget you’re spawning with the component. Like Jared said, just use the cast. Casting should work, may not work on Construction script time (because I don’t think it’s created yet), may need to wait until Begin play, that’s what I use in all my tests and works fine.
The blueprint node that you see is super special, the node is actually generating all the setter nodes + the actual construct call based on the exposed properties when the blueprint is compiled.