How can you cast a spell at a caster level much higher than 20?

Certain spells such as Mass Cure Critical Wounds have level-based effects with caps that are higher than 20 (in this case, 40). How is it possible to cast such spells and have the higher-than-20 cap actually matter?

I know there are some relatively uncommon ways to boost your CL by a little bit (e.g. Orange Prism, Moon Circlet, and Improved Caster Level, although ICL doesn’t give you a bonus higher than your character level, which makes it irrelevant for this), but these are tiny bonuses. Is it even possible to cast something like Mass Cure Critical Wounds and heal for the full +40 hp?