Force Substitution (3.5e Feat)
From D&D Wiki
Force Substitution [Metamagic]
Prerequisite: Must be a spellcaster that can cast at least 3rd level spells.
Benefit: When you cast a spell that does elemental damage (fire,acid,cold,lighting,sonic) you may make the the damage type into force. This metamagic doesn't increase the spell level of the spell.