Hey Peter,
There is space on the front side of the pedal to add a 2nd 1/4" jack. It's actually the output side where space is really tight (you've only got +/- a couple millimeters in any direction to play with as you need to drill a 10mm hole for the jack), so theoretically, it should be possible to use two external latching switches.
Personally speaking, I wouldn't bother to modify the pedal for effect on/off though as the blend control can be turned right down to bypass the delay line...