Not an expert either, but if such a thing was allowed, you could arrange to buy expensive stuff you want to have on a regular basis (I would assume this is not

Not an expert either, but if such a thing was allowed, you could arrange to buy expensive stuff you want to have on a regular basis (I would assume this is not uncommon for CEOs) and then just agree orally with the seller to cancel the transactions when the stock is down, go through with it when the stock is up.