Haven't really seen any good info on this, I have done quite a lot of these, the truss rod nut strips, and you have a walnut plug in the way... What to do...
Well the way I fix these, I start by steaming out the walnut plug, score the finish around the walnut plug, then drill a small hole that fit your steam needle tightly, be careful not to drill all the way through, into the maple, you just need a hole so that the steam will saturate the walnut and soften the glue..
Let the steam work,when you see bubbles around the walnut plug, you need to put pressure on the plug to drive it out, I use a screw extractor to unscrew the truss rod nut this will drive out the walnut plug..You can also pull the walnut plug with a little hook of some kind, have some dentist tools around for that kind of thing..
Once the plug and the nut is removed, I clean out the truss rod cavity and maybe chase the tread with the tool I have very similar to the Stew Mac truss rod rescue kit.
Steaming out the plug leaves a nice clean hole.
I let the guitar sit for a day or two to get all the moisture out.
Put on a new Fender replacement truss rod nut
Then I make a new walnut plug on the lathe, and tap it in with a little yellow glue..
Trim it to size and a little finish touch-up and here is the finished result..
My steam needle is a "standart" Stew mac needle, I have no problems with finish from moisture, normaly I don't need to steam more then a minute :)
Yes I am happy to share tricks and tips..
I think you are right, 3mm allen key is close.. I know that fender sells replacement plugs, but getting one here in Denmark is just silly they do not stock any parts that is not sold by the 1000.. :) :)