Graphical 128x64 uext display contrast adjustment?

The “documentation” for the GRAPHICAL 128X64 UEXT DISPLAY doesn’t talk of any way to control the contrast. Is there any way to do this. The contrast is way too high out of the box, especially since I’m now controlling the backlight via PWM and it may be a bit dimmer. Thanks.

This is the internal controller datasheet.
http://www.tinyclr.com/downloads/Extension/SPLC501C.pdf