Beat me to it.
Arduino supplies the right voltage. Set an Arduino PWM pin as output, tie it to the driver's PWM pin. Do an AnalogWrite with the value you want. Try out some values. It should actually be very easy. Jameco gives that part as 6 weeks. You are a more patient man than I am.
It's out here too:
http://www.powergatellc.com/mean-well-ldd-600hw-dc-dc-converter.html
Out at Mouser and twice as expensive:
Why do you want this part in particular?