E.I.
the thing that worked for us is just waiting and NOT pushing in any way shape or form. usually our son would come into the bathroom with me (sometimes my husband) and usually then he would sit on his own potty, whether he went or not didnt matter, he was sitting there "acting". its amazing; when a kid "gets it" by himself its more effective than when we "push" them to do it. with my son, who is extremely self motivated, if we MAKE him go, its torture, he flips out, and it just isnt going to work. when he has to go and does it on his own, it works beautifully. hes trained himself.
from what it sounds like, you are where my son was for a while. just do your best to do what you have to do to get him to go. the only way he is going to learn is to just do it his way. if you have to go somewhere, realize that you can try to use underwear, but you are probably more safe using a diaper. and big deal? it wont deter him at home (usually). i would rather do that than have to deal with my kid and him peeing on a store floor... (he did that in the dog food section of L&M once).
anyway just take it easy, do your best, and dont stress. he wont go to school in diapers. lol