The reversing Y will only reverse the servo. For elevator you need something more sophisticated, either mixing or one of the Matchbox/Equalizer gedgets.

I have not yet tried the Equalizer, but I have used both mixing and the JR Matchbox. Both work very well. The nice feature of the Matchbox is you use just 1 channel for up to 4 servos, whereas mixing requires a separate channel for each side. The Matchbox allows you to change reversing, adjust the center and the end points individually for each servo with them all on the same channel. The Matchbox also has a port for external battery hook-up. All of this results in a fairly steep price, $79.99 if you buy 1 and $55 is you buy a pair. The Equalizer has a 2-servo version that runs about $50, as I recall.