Let us know how it works out for you. I would be a bit nervous about keeping a constant 15V to 18V on the AM engine for a long period even with it in neutral. In theory its ok, but one minor jostling and it will take off full speed.
The easiest but not the most elegant alternative is to buy some 6-49858 transition track pieces and use Gilbert turnouts. The power routing feature allows only the selected section to be powered with no rail gaps required.