If you mean engaging the break away cable, it's not like your parking brake on your vehicle.. The trailer wheel will need to turn just a bit to engage the shoes from the magnet that is now locked on your drum.. Not really a good way to do that if it were me..
What I would do is get out my level boards and build up enough height to pull the blown tire on and that should put enough pressure on it to bust loose the lugs and then you can jack up or use whatever other method you would use to get the wheel off the ground to change the tire.
Good luck!
Mitch