I have 2 daughters, so I don't know much about the differences between potty training boys & girls. For my first daughter, letting her wear a pull-up or diaper while we were training did NOT work-- she just waited until I put the diaper back on to pee. So I chose a long weekend that we were going to be home the whole time (and it was a comfortable temperature in the house) and I set her potty chair in the kitchen. Then I let her run around the kitchen for a day & a half with only a shirt on. Whenever she had an accident, I just said "whoops!" and rushed her over to the potty. I had her sit on the potty while I cleaned up the floor (and her) and told her next time she needed to go, she can run over to her potty chair. All of this was very light-- no expectations or disappointment or frustration-- just a fun game. By the end of the second day, she had it down pretty well and was wearing undies (I found that at first, the training pants felt too much like a diaper, so we went with thin undies and then went to training pants once she had it down pretty well).
I have also heard of people having success training their boys by letting them pee on trees in the backyard (the boys thought that was really fun). They then, of course, had to make it clear that they don't do that all the time. ;-) But it at least worked to get the boys to learn control. Good luck! This is definitely a challenge, but it will happen eventually.