Having been playing around with JComments recently, just building a list on top of the main JComments 'comments' table wouldn't work for adding comments, as there needs to be an 'object' in the JComments objects table that owns the comment(s).
And there is no actual API to be able to insert objects and comments in JComments programmatically. I had to write some custom code for a client a few weeks ago, by copying and modifying a big chunk of JComment's code, to create the object, and add comments to it.
However ... whilst writing that code as part of a custom plugin, it occurred to me that the code could be integrated in to our 'comments' form plugin, to allow automatic creation of a JComment object when adding a new form, and / or automatically adding content from the form as a comment to that object, or some other JComment object, although I'm not sure how we would let people specify which object to add to, if it wasn't to the object specifically associated with that row of that Fabrik form.
So that's the good news - I know (mostly) how we could do this. The bad news, it isn't going to happen any time soon, unless it's done as a custom job for someone. It's not something I have time to "just do" right now, and isn't something covered by a Pro sub.
-- hugh