How can I wean DS off rewards for potty performance?!

[MumofJTM]

My DS is 2.8 and we have been potty training for nearly 4 weeks - generally going pretty well. From the start he has been rewarded with choc buttons/ smarties etc when he produces something in the potty. Since returning to nursery after holidays he has quite hapily performed without choc, as I told him ot wasn't fair on the others if they weren't allowed choc and he was. However, at home he always demands his reward, and has the screaming la la's if I suggest that he doesn't need one/can't have one.

My question is - how do I cut out the rewards? Or just grit my teeth and buy more smarties? I just can't see him forgetting about them? How long should i go on rewarding him?

Help!!! Any ideas gratefully received!

Can you replace the chocolate with a sticker? Maybe to stick on a chart - 4 stickers and he can have a big chocolate for pudding after tea. Then you can run out of stickers, but 'Mummy will remember, and you can still have your treat after tea' - eventually, treat just becomes whatever dessert you would usually offer anyway.

We put our choc buttons in a glass jar on a shelf to help motivate ds1 whilst potty training. When I wanted to wean him off the rewards I made sure there was only one left and so when he had that I made a big deal about "Oh no, look there are none left" etc, etc. Then, as JennyWren suggests, I said "oooh look how about stickers instead?" He gets amazingly excited about choosing which colour star to put on his chart.
Now once he's filled a whole line of stars he can have a choc biscuit. It seems to be working well so far....