It's almost impossible to make a T-molding groove with a Dremel.
Unlike a router, there is no depth setting on them.
That means that you would have to freehand right down the middle of the entire piece, to get the T-molding to fit properly.
Unless you have alot steadier hand than anyone I've ever met, you're going to end up with a wavy groove, which will make the T-molding stick out to one side or the other in places.
I would also question if the motor has enough torque to cut that much wood without burning itself out.