Only by text()'ing the multiplier in to place, and being sure to have that logic hooked in to zoommode() so that the multiplier gets updated as you zoom or pan around.
There is an alternate approach, which is to set the [XY]TickLabel directly, to a tex string that includes the exponent in it. Having even a single [XY]TextLable turns off [XY]TextLabelMode, and with that mode turned off, it will never include the automatic exponent, leaving you to text() in the entire label yourself. Though again if you do this then you have to handle all the label updates in zoommode(), but at least you are saved from try to get nice pixel alighment in the add-on string representing the exponent.
