As far as I know, there is no direct way to do that. I think, there are two solutions. You could merge the table cells and leave the whole RadioButtonGroup together. This could lead to the problem, that the vertical borders won´t expand automatically, if the row increases it´s height.
Another option would be scripting. Just use a hidden field holding the value of the "group". You would have to check/uncheck all radios accordingly.
Both variants aren´t very sexy, but will solve the problem.^^
Greetings,
Joerg