Google knows everything. I found this:
Snubber Circuits Suppress Voltage Transient Spikes in Multiple Output DC-DC Flyback Converter Power Supplies - Maxim
it is an app note from maxim regarding snubber RCD and RC circuits for use in mosfet driven flyback transformers (similar stuff to what we're doing here). I gave it a skim and it seems simple enough... I'd run it by our lab tester, though.