318 expansion plug leaking

Why not pull the engine and get it done, its a weekend job or 1 day depending on how you work and how many times you've done it. Think about the time you will spend playing around trying to make a tool to get at it, you could play around for a few hours and get nowhere, when you could have the engine out on a stand in the same amount of time. Also as mentioned, the "temporary" screw type plugs also work when you don't have the time to pull the engine. In the case that the car is your only daily driver the screw type repair may be the way to go.