Custom mounts

Hello everybody.

I would like to create custom mounts by using these creatures:


What I did:
Set the integer bX3_IS_MOUNT to 1 on the creature.
Set the integer X3_HORSE_TAIL to the corresponding number in tailmodels.2da.
This works at his best on modeltype F (full) based creatures.

The problem.
90% of the creature are modeltype S (simple) based creatures: this means that once mounted, the creatures appear completely rigid in game.
Any way to convert them to modeltype F or other suggestions?