I would recommend coco nibs, and some coco powder Alkali free. This will give the range of chocolate flavor. If you have a local chocolate shoppe go ask if they have any nibs or anything you could make beer with they might hook you up.
Think of beer as food Trippels are malty, rich, complex esters from the yeast and a beer you want to enjoy! So now you add chocolate a mix of Bannana Esters rich malty ness with a smooth rich chocolate with just a bit of bitterness.
Myself I would even be tempted to hit it with a shot of Bannana Liqure just for fun.
Never made one but you talked me into it. Use a Belgian High Gravity and start it at 11% OG, mash at 150F-152f to keep that great body, and malt.
Oh and send me one thanks