I'm not sure if you can embed surface metal raceway like 500 in concrete and plaster that way.
But anyway, what about just running MC cable in the channels and slipping a piece of solid back Superstrut over it backwards, like a U-guard. You could miter the strut with a band saw to make the corners and use some Tapcons with perforated strap to secure it in place until the mud gets troweled over top. You should have more luck meeting the bend radius for something like 14/2 or 12/2 MC than EMT.