How about not cutting the -ve or +ve but decreasing it slowly
"The current within the electronic ignition example shown sharply rises to 6 Amps, at which point the current is held until the earth circuit is removed. The switching speed can be seen by the angle of the vertical line at the end of the trace, any delay or slow switching will be seen as a sloping line. Any compromise in the switching speed will result in a lower induced voltage."
coil basics

with a view of creating less HT voltage that is not strong enough to jump the electrode gap