Not know any details about what Dan is trying to accomplish other than making showing repeat region balloons easier to show and position, all I know is you can't explicitly do what he is asking. Now, if he is open to other ideas about getting balloons on a drawing, there are a myriad of ways that can be accomplished, each with their own advantages and disadvantages.
I would also agree with the "specification" for BOM Balloons includes "scattershot" and "frustrating." I know how to manipulate repeat regions and I know how to manipulate bom balloons and I feel like I can do just about anything I need to do to get my drawing to look the way I need it to look but I also feel like I can waste SO much time on it that it's just not worthwile. At my current job, there is no requirement to use repeat region BOMs and balloons. I use them when it's easiest to use them. I don't when it's going to be "scattershot" and "frustrating."