You can use X Core, just have it roll the dice and the middle dice in the output is the Marvel Dice. If it comes up a 1 you'd have to manually add 5 to make it 6 but that's not too hard. I don't know a way to do it in FGU without coding and extension. Alot of the stuff would have to be done manually - multiplying the damage and stuff like that, but it would work as a start.

