Without the Bat. Is it possible? He has tons of HP, so I'm not sure if you can hold enough stickers at that point in the game to both take all 300 out, take out his pokey partners, and keep yourself healed.
If it is, does Kersti scold you like on the Megasparkle Goomba?
It's possible. I didn't have the bat there and didn't feel like resetting the game and go back to get it. It takes time; yes, and LOT of stickers, and you need to block pretty much everything. but still possible. Meh...Mushrooms help in the pinch, but you're pretty much in trouble if you run out of stomping stickers while he still has his body parts up.
The way I did it was first use all my stomping ones, a.k.a shoes, on him. Used something like flowers when he spammed those little minions and once it was only the head; went for hammers.
EDIT; and yes; Kersti WILL scold ya. She does it every time you use lot of stickers in a fight and don't use those special stickers that the boss is weak to. Nothing to feel bad though IMO, but...Yeah. She will nag at you.