You might wanna try top knot gel, but I don't know how well it would work. The hair on the booty gets bothered a lot, with sitting and laying and everything. Uni gets curly butt too. When I dry her i try to use a brush and the hair dryer to smooth out her hair, like giving her a blow out, but if she doesn't sit still it's very hard. Or even if she does sit still I can't get the hair under her butt. I need her to stand still.
Anyway, Mimimomo sells top knot get by Pet Silk I think, you may want to ask her. Or Maximo, she sells Pet Silk too, but don't know if she stocks the top knot gel.