I am sorry, English is not my native language. I want to suggest to create the invisible character that it was possible to make thrusting without the partner. All "drive" sliders will be enabled, and "force" blue arrow is still there, but no visible guy.
And parenting for the characters base will be good.
Comments
http://forum.yiffalicious.com/discussion/comment/915/#Comment_915
The response was "Not a bad idea but not a priority.". There are quite a few interactions, though, which bypass this by hiding the "invisible character" within an object (e.g. a wall) or by using the POV option (like "Sub POV Blowjob" by LordPorker). Just look around the Cloud if you need inspiration. Also, Imagination is key. Those apply to Yiffalicious in general.
As for tribadism, I have absolutely no idea how that works so I can't speak about it.
Now, of course having "native support" for these positions would be better in the far future, but I assume making a character invisible would be easier and quicker than actually implementing the other poses, so it could work as a stop-gap until the other poses have been completed. And even afterwards, I am sure people could find interesting uses for this.