I think this would work:
Go to Game_Enemy, and look for def base_maxhp.
When you get there, Comment out the original (in case this doesn't work), and put this in:
def base_maxhp
return $data_enemies[@enemy_id].maxhp
if [INSERT ID HERE] then return [NUMBER HERE]
end
Again, not sure about that, but it's the best thing I can think of on the spot. Also, you can adjust this pretty easily for SP, or any stat really.