Looks like you already have big tires aired down. That's the #1 thing that will affect comfort over any kind of chatter, although I don't know if the WTB Riddler is a particularly plush tire.
The other things to consider here are a carbon seatpost (guessing that bike has an an alloy one stock), which will dramatically reduce the buzz going into the saddle, and thus, your body. You also need to make sure the bike fit is good with your saddle positioned / tilted correctly so you don't lean additional weight onto the handlebars that will cause discomfort / fatigue in your hands. Someone already mentioned the "loose" grip as well. One of my favorite positions over really buzzy terrain like washboards, or tractor tracks on dirt roads is a loose(ish) grip around the drop hook that allows the front to bounce some in your hands, but still have total control. That, combined with standing slightly on the pedals (in straight lines) can give you a lot of suspension, without suspension.