Obligatory blah blah blah . . . won't taste as good . . . gastronomical philistine . . . fer seriousszz!
I suppose if you really wanted to cut it down;
1/2 cup molasses
1/3 cup soy sauce
2 tbsp chili powder
1 tbsp garlic powder
Splash of water
I'd also stab the shit out of the roast with a fork before marinating it and extend the soak time to 24-48 hours.