you're correct: a few of us have narrowed this odd occurrence to a leaking intake manifold seal(s). If the dipstick is removed (good logic to follow there), there's another air intake source for the leaking crank case to draw from.
Apparently if the intake is leaking, vacuum draws leaking oil (from the crank case) into the intake system where it apparently ponds over +20-30 seconds until you mash the gas & an influx of air sucks the oil into the combustion chamber resulting in the oil & smell.
Thicker oil will help reduce the oil being sucked into the intake and the reason this happens at idle is because vacuum is at it's highest and that air flow into the engine is at it's lowest. Punching it after idle drastically changes air volume into the engine which sucks the oil into the ports.
You need to spend a few hundred & have your intake manifold re-sealed (removed & replaced).
People spend thousands on having a valve job which also fixes the problem...why? Because you have to remove and reseal the intake as part of that process.
Mark