Easy way to do it? No. Is there a way to do it? Yes. At least, you can do it for PCs. There isn't a way to alter the NPC crit tables (except maybe with API, I don't know). For PCs, go to the Attacks and Damage section, open up the first entry with an attack roll. After the damage type there's a section for Critical, which defaults to blank. Blank means it simply repeats the calculation in the initial damage field. If you put anything in that field, though, it will override that and instead do what you put in that field. So if you put the maximum amount of the standard damage in that field (like 12 for a greatsword), it will roll the regular damage in the first section, then say +12 if a critical was hit.
