extension

My plumber installed the rough in for my shower head arm too far back in the wall and the shower arm only sticks out of the wall 3 1/2". I would like to increase that length. The rest of the trim is brushed nickel from American Standard and they don't make a longer shower arm in that style...

This one should be an easy answer, but I can't seem to find it (I'm probably not using the right search terms...), so any help/redirection would be appreciated! I'm putting in a shower-over-bath in an alcove, and, lo and behold, after the tiler put in the tile, when I came back to put the final...