trying with this one but cant think of a way with it been HT and not so managable. Thinking about maybe something around the HT lead coming from the coil so that when the feed to the coil is broken and thus transfering to the secondary ready for the next impulse it switches in a burden on the secondary side limiting its path. Cant think what though and not sure it would give the full kill you require.
Only other way would be to ground the HT lead prior to it reaching the spark plugs, when required, but again as nothing is readily available it would be a botch up and a) not work and b) look shit.
hard one, i'll sleep on it and probably wake up none the wiser