I'd like to extend Group Summary Plugin with a new GroupSummary type "button" that would after click change all fields in the given column and group (say set them to zero etc). It could be as simple as adding a new field in GroupSummary.Calculations like

'setToZero' : function(v, record, field, data){
data[field] = 0;

but how to make this new summary type active (clickable)? Please advice how to attache corresponding handler and where to put it into Group Summary Plugin architecture. Thanks a lot.