I "borrowed" one of my daughter's black elastic hair ties and wrapped it around my lighter under the gas button.
After wrapping it several times the tie builds up enough to keep the button from depressing.
It's easy to remove and easy to reinstall.
That is pretty much what I do for my every-day carry mini-Bic. So far, after several years riding in my pocket with very occasional use, the lighter is still mostly full. Seems to be working.