I use big screw eyes with a washer inside in the tire, then a sturdy snap or caribeener on the end of a rope which is attached to the trace. You want those tires WAY behind the hind feet, so that if there is a blow-up, someone can safely detach them.
We use a big, fat cotton rope, about 25 ft, wrapped through the bridle around the nose for a helper to hold, because the driver has enough to mess with, and the helper can pull a panicing animal off balance a bit, if needed. We use this all the way through first carriage hitch-up.
Say whoa immediately after the first step they take with the weight, and that way they learn stop is the release, not run.
Remember to have a helper that won't panic if something goes wrong. if anyone panics, quit immediately, and find someone else.