matrixctrl & radiobutton behaviour

Hi,

using the "one non zero cell per column" behaviour set in the inspector i can use the mtrixctrl as radiobuttons, which is great but is there a way that it´s not possible to deactivate the current pressed button?

At this point it´s possible have no buttons activated, i´d love to change it so that one button is always set to "on"

thanks for any help :)