As far as I can tell from the pictures of The Kick that I've seen the wire solution would be best with the Grand.
For this we would dedicate and hard wire a Kick to the Grand, because the spring will not make a solid contact with the ground thus rebooting the micro processor often, resulting in intermittant firing.
So I am proposing a simple add on to be able to use a Kick in a Grand: We would take a small aluminium tube, 19mm inner diameter, length about 15 mm. This tube would have a wire (thin would be ok, I am thinking that the ground is just for the micro processor and electronics, not the work power) soldered to it, that wire could then be threaded along the side of the battery to the ground spring of the Grand. There it will not be soldered, but instead simply fastened under the spring, which can be loosened by a small phillips (is that a Kreuzschraube?) screwdriver.
Soo, now I can go hunt for an aluminium tube - after all I AM a German engineer and one has to live up to standards, no? *grins*
Edit: Plus, this would make it work on a woodvil too, plus, no permanent changes to the Grand.