Personally, I would have put "obsessively" in brackets, preceded by "almost", so the line would have read:

... and the editor, (almost obsessively), inserted huge numbers of commas into my pieces.

"obsessively" just needs some qualifying here in order to read smoothly IMO.

I don't think the editor, no matter how obsessive, would actually have inserted a comma between "commas" and "into".

I just love threads about pedantry ...