forget the potty, he doesnt see you or anyone sitting on a potty so it doesnt make much sense, it sounds as if he is aware of when he needs to poo too which is fantastic for such a little fella, this will happen naturally for him.  sometimes kids get a bit frightened about their motions falling into the toilet so let him take his time.

there is a wee man toilet trainer that you can get that attaches to the side of the toilet.. he can stand and wee in it.. then you just flip it over and flush... my boy loves it

If your little boy is keen to use the toilet I would not worry about the potty. Get him a little step so he can reach the toilet and you can also buy little toilet seats to place under the normal one for when he is sitting on the toilet. I think introducing a potty now when he knows how to use the toilet would only regress things.

also remember to give posative encouragement when he does use the toilet.

place the potty infron of the toilet where he likes to pee, and put a ping pong ball and get him to try and aim for it.

this also works for older children using the big toilet as the ping pong ball doesnt go down the drain when flushed

 I was worried  my son would'nt learn to pee pee in a toilet as all he has is mummy all day when i discovered these....http://www.greatdad.com/tertiary/381/1403/peter-potty-stand-up-toilet-training.html maybe this will help ?

hugs jo xxx