Make Spellvamp grant 100% healing on AoE abilities-
-but only heal you from the first unit hit.
The biggest problem with Spellvamp is that it's really only useful as in-combat healing on champs that have mostly single-target spells (see, Jax and Akali) while being someone silly for out of combat healing when you can just lob a nuke into a pile of six minions for a massive heal. So why not just normalize it?
treatment.
There's also
. It only work with physical damage but as far as I know it fully apply on AoE spells.