This one was supposed to be a bit more robust but I kinda ran out of steam so I'm presenting it as is. It facilitates futanari using an onahole on just the tip of the penis rather than it being mid way or fully enclosing the member.

Anima:

Supports "Opaque onahole" and "translucent onahole" along with colors. You might need to add "artifical vagina" to your prompt for some checkpoints.

Main Triggerword: onaholing

Secondary Triggers: opaque onahole, translucent onahole

Illustrious:

I tested this a long time ago so I don't remember if it has any weirdness to it but I don't think it does.

Triggerword: onaholing

Triggerword(Fleshlight Version): fleshlight

Side note: I do take informal requests(basically a bounty that you don't have to pony up buzz for) if I like the idea(Tips are nice but not required since if it's a good idea then I'll get generation Buzz). Just leave a comment on one of my models or DM me. (Comments are preferred since that let's other people see that I'm actually fulfilling informal requests.) DMs are perfectly acceptable if your request is a bit out there and needs some image examples or something. As a note I will probably pass on Manhwa characters because I generally find their designs to be kind of bland.(No shade to Manhwa creators, I know many of them are going for regular releases and intricate designs are not what you want in the case.)