The PA900 supports half pedal with the use of the Korg DS1H.
The PA900 also Lets you change the polarity of a pedal in the damper plug and it supports variable pedals in the assignable plug on the back.

The Roland RPU-3 has 3 variable pedals in a Piano configuration. If I plugged 2 of the 3 plugs into the PA900 would it work?

It would be nice to have a Sustenuto Pedal that looked like one!