Checkbox Selection Override within Architect

I found the following in an old thread that looks perfect for making he checkbox selection model behave as if CTRL is always held down. Where would I put it in Architect? I already promoted the grid to a class and have an override for the rowexpander plugin (screenshot below-below):

Ext.grid.CheckboxSelectionModel.override ({

handleMouseDown : function(g, rowIndex, e){

if(e.button !== 0 || this.isLocked()){

return;

}

var view = this.grid.getView();

if(e.shiftKey && this.last !== false){

var last = this.last;

this.selectRange(last, rowIndex, e.ctrlKey);

this.last = last; // reset the last

view.focusRow(rowIndex);

}else{

var isSelected = this.isSelected(rowIndex);

if(e.ctrlKey && isSelected){

this.deselectRow(rowIndex);

}else if(!isSelected || this.getCount() > 1){

this.selectRow(rowIndex, true);

view.focusRow(rowIndex);

}

}

}

});

Capture.PNG

Thanks,

Gerry

Checkbox Selection Override within Architect