Serious question. Instead of casting the net of random checkpoints that ensnare plenty of people who haven't been drinking, why don't LEOs conduct surveillance of a bar each weekend. Post an officer with a radio near the parking lot, have him ID drunks driving off the lot, and have a pre-staged cruiser follow the drunk until he commits a moving violation, then stop him and get him.
The operation could move from bar to bar, even on a published schedule, so no one business could complain about unfair targeting.
Seems like shooting fish in a barrel is better than casting the net.
If it jams, force it. If it breaks, it needed replacing anyway.