Sorry for the delay.
You can set the mass per component by using a Physical Material Override but the component must be simulating physics for it to have effect. So attaching non-simulating components to a simulating body wouldn’t work.
To accomplish what you want, you would need to use Physics Constraints (this is what they are made for). I know you said you heard bad things about them but I just created a simple version of this in a test project and it works quite well. You just lock all Linear and Angular Limits on the Physics Constraints.
Since this is getting off topic from the original bug report; if you need further help, could you post a new report in the Blueprint section of AnswerHub. Feel free to link this post in the description and PM me a link to the new report over the Forums. I’ll be glad to continue helping if I can.