I've seen the suggestion to make DE a buff/aura on the player, but what about the idea of making it a reactive debuff you cast on the target? So like, you cast the spell on the target, they have a 20 second debuff or whatever that makes any of your pets that attack that target gain 50% health and haste for a small duration, refreshed every time they attack. It would solve the problem of having to recast it every time you summon imps or dreadstalkers, at least.
I actually can't recall if the "creatures that attack this target gain X" debuff mechanic has existed in the game yet, though.