Since my polymorph meme has only garnered three downvotes so far I thought I'd offer a bit more controversial take, and see if I can manage to stir the pot a bit with this one.
I haven’t found a solid contradiction to this plan in the rules-as-written.
If you read Vampiric Touch it's literally in the first sentence:
The touch of your shadow-wreathed hand can siphon life force from others to heal your wounds.