Hi I would like to know if there is a way to do 'exploding dice' as follows: Roll 2d6, then 'roll up' an extra 1d6 if BOTH of the initial d6 rolls are 6s, AKA 'Boxcars'. I can only see how to 'roll up' for ANY d6 rolls that are sixes, and this isn't what our system does. We are using BESM 3rd Edition, BTW.