The secret to the fatty melt is to start with two very thin grilled cheese sandwiches to start and only to add the patty when it has cooled down a bit and is not greasy.
Try plain white bread, like webers, and one slice of american, swiss, or pepperjack. If you're grilling it in a pan put a sheet of foil on top of the sandwich and press down using another pan or a heavy pot. repeat on the opposite side of the sandwich.
From here, I don't add much, a little mustard and a thinly shaped, slightly cooled, and not greasy hamburger patty, press down again...eat. eat. eat.
I have also seen the "club" idea before. Not to be taken lightly. This thing is BUSINESS. For that guy, there are three grilled cheese sandwiches as buns and each sandwich has two slices of bacon grilled right in with the cheese.Between each sandwich is a big ol patty. Hardcore....I'd eat it. If noone was looking...judging me...
The website "this is why you're fat" .com also has many variations for you to study. Again, please let us know if you try again!...pictures?