E.M.
Hi C.-
2 thoughts: He probably needs a stool to stand up on so that he can reach over the toilet without peeing on it. The other thing is to make a game out of it. Drop cheerios or fruit loops into the toilet and let him "aim" at them. Give him points or let him earn something for peeing standing up. Say, going potty sitting down is one point or marble in the rewards jar, and standing up is 3 points or marbles. THis way you are still reinforcing his potty training, but allowing him to try it another way with a reward behind it. Plus, as he gets older, we all know how unclean public toilets can be...and standing will be cleaner all around.
I hope this helps!
-E. M