Also, idk I am allowed to here, but I got an idea.
Maybe you can select from different types of Tentacles? Like, one is a basic "penetrate" tentacle, while another type specializes in nipple simulation? Or maybe a tentacle that mimicks the target, but with a tentacle sticking out from the crotch... Have the target take their big membered doppelganger? Idk.. just some ideas.