Adding dice rollers?

For some reason, I’m not seeing how to add additional dice to a game.

I’m looking at the Axis and Allies Vassal implementation, and it has a button to roll a d6. When I try to edit the file, I see how to edit that button, change the type of die, etc. But I don’t see how to add additional dice. What am I missing?

Ultimately I’d like to add a button for each of the following–d8, d10, d12, and d20. This is because I’m thinking about implementing Conquest of Nerath in Vassal–and it appears to me that this might not be too hard to do simply as a slightly-more-than-reskinning of Axis and Allies. (Adding the cards will be the hardest bit I think.)

Right-click the top [module] level and select Add Dice button