Well I sure wasnt expecting a reply 2 years later lol
I actually mentioned in the post:
And trying your suggestion has the same results. Massless = true and low Density still have an effect on the character, and it makes the part super floppy.
I do actually have a solution though, I guess I never bothered to go back to this topic and making a solution. Around 7 months after this topic was created, I just tried writing code to do this exact thing. After a lot of headaches, it actually worked.
Here is the basic rundown of how it works:
I use a Spring module to create a spring at the position of the part.
I get the Vector3 difference between the part position and spring position.
I rotate the Bone/Motor6D/Weld based on that position difference.
I set the springs target position back to the part position.
Done.
Obviously there are more things to it, but thats just the basics.
If anyone wants to do this nowadays though, I would recommend SmartBone instead. Its a lot easier to set up, and you dont really need to write any code yourself.