Well, I am quite close to Cod in method, but if tomorrow is very important to you, then I would say bung a nappy on him and enjoy your day. Don't worry about his age. Mine were about 35 months, 33 months, 37 months and now my youngest is 30 months and being potty trained. The later you do it, the quicker they seem to pick it up IMO. I know a lot of people say don't put a nappy back on them once you start training, but I have always done it for certain reasons (eg today, we had a three hour journey to make so ds3 wore a nappy for that). It doesn't stop your ds from asking for a potty if he is so inclined. My ds3 wears a nappy at night and keeps it on when he first wakes up but often (lately) has been taking the nappy off to wee in the potty. The only thing I find is that sometimes, when he has been wearing a nappy, when it first comes off, he forgets and wets himself. Today, after our journey, his first wee was on the ground (luckily outside) but then he did 4 wees in the potty and one in the loo (his request) before bedtime.
Do you try rewarding him for success? I am shameless. It is one chocolate button for a wee and 2 for a poo and ds3 knows that and rarely forgets to ask for them!