The only way to catch those solo big boars... is with a sow in heat. They get real stupid... as do we all. :D If they aren't in the trap... you will pop them with a rifle while they are circling the outside of the trap.
When you catch the sounder pop all the little pigs with a .22 and get them off the biggest sow, or couple of sows. I think getting the pigs off probably makes them cycle just like pulling calves but not sure about that. You'll show up and have two boars in the pen fighting and one on the outside trying to fight the fence to get in on the action. ;-)
When the pig hunts were real popular and people were fencing off land to hold hogs and sell hunts the biggest amount of damage done to the fence was not from the hogs on the inside. It was from the single boars on the outside tearing up the fence trying to get to the sows in heat on the inside. Its just like bulls. You get one on the inside and one on the outside and they will destroy a fence. I had some friend that had a place. Every day they would drive the perimeter shooting boars that were fighting.
Using pigs to catch pigs is a tried and true proven method that just flat out works based off behavior no matter if its wet, dry, deer season, not season, trap smart, not trap smart... it works. It not only works with hogs... it works with cattle, people, and most other animals. :)