I would highly recommend NOT doing something like using a threaded pad in a threadless setup.
The threadless setups are commonly called "Cantilever-Style" because cantilever systems are almost ALWAYS going to use the threadless type of pads, except those that specifically say "Cantilever V-Style." If you look on eBay, you'll find this is true if you search 'Cantilever Pads' versus 'V-Brake Pads'.
Where you said you had trouble stopping because it took "quite a while to stop," I'd say you either have a bad set of calipers, bad brake levers, damaged cable housings or bad housing stops, as there should be as close to zero flexibility in the brake system. The pads should be 1-2mm away from the rim before you touch the brake lever if they're well set up on a decent set of trued wheels. Then, pull the lever until the pads lightly touch the rim. Then, watch the caliper arms and pull the lever as hard as you can. If you are able to see flex that allows the brake to touch the handlebars, buy a new set of brake calipers or a new bike, because too much flex is ridiculously dangerous.
By the way, I HIGHLY recommend changing to V-Brake style systems, as I personally find them far easier to work on. Those pads, the Clarks Elite Tri-Compound, are literally the same ones I use. Be wary that you'll find an increase in the frequency for replacing them, as they're made of a softer material, but note that the power and the reliability that I've had from these pads are well worth that trade-off.
Good luck with either you choose, but please do not try to bodge the two worlds of V-Brake style and Cantilever style pads into one.