I'm not sure that is possible. Or that you would really want it if it were.
I think all elements in an EGP operation need to be set specifically for that use. Think of deploying that asset then to other users ... Premiere would have to move that entire video file along with the rest of the items in that graphic.
Which would make the size of that mogrt ... truly, wastefully, massive.
By doing this I dont have to nest and I am able to create a mogrt that has the video connected. The problem I have sometimes the opening animation is not needed and I cant just move the in point past the animatuion . The only thing I can do is nest it.
For use in mogrts, I think the best practice is to use a clip prepped for that use. An actual clip, to the right length, with any effects needed on that clip baked in, exported/imported.
That keeps the mogrt "light" as it can be, and seems to save hassles down the road.
But the other way I use it as just as a Graphic and not a MOGRT. so I dont have a nest because the are pain to deal with. By being able to keep the video and gfx togethere its more compact. If I have to do a recut of the video everytime that wastes time and space.