Have to agree with Wally. The only route for oil to get to the top of the pistons is via the rings or the valve stem seals. Even if they were very worn, it would take a very long time for the bores to completely fill with oil. Maybe if you chucked the oil down the spark plug holes...
Oil gets on the bores to lubricate them via the oil control rings (ie the bottom ones), which are in turn fed via holes in the pistons. The only way you will get oil above the piston crowns is if you deliberately pour it down the spark plug holes - which is the correct way to preserve an engine, as it happens
Or if your valve stem seals are completely knackered.