That is a bit of a shit act but as you say if he's not a bad bloke then best keep him around..

The ping pong ball in alfoil is a wicked smoke bomb..
But usually lit with an open flame..
I'd say best chance of light up would be the manifold.. but if he's still got the factory heat shield I doubt you'll get anything in close enough. .

I am personally liking smoke in exhaust and brake light horn..
Both easy to carry out with a great outcome..

If in the high country a limited rpm range may become dangerous on some of those tracks...