How do I have Alternate Form increase a non leveled Advantage?

[Armin]

I'm sorry, but I don't understand the question. Regeneration does have levels, going from Slow to Regular to Fast and so on. It doesn't have uniform costs per level, but that doesn't matter to it receiving level bonuses.

As for a "proper" way, any way to do something unusual that results in you getting the result you want in a way that you understand should be just fine.