Hello. We recently installed new tile in a customer's shower surround. We also replaced his old shower vavle with a new one. After installing the backerboard and tile, we discovered that the stems for the hot and cold handles are a little short so we can't install the new handles. The handles are held on by a small allen/hexhead screw.

Is there a way to extend these stems a little bit so we can get the handles on? The new valve is not a name brand. It was purchased off of ****.

Thanks for any advice or help!