Have you tried simply immersing it in acrylic resin? I imagine the chief issue won't be from typical chemical oxidative decomposition, but rather from photodecomposition.
Perhaps you might try dessicating/freezedrying the samples first (in a vacuum), presuming it won't affect their appearance too much?
EDIT: This is a hipshot--perhaps try putting water glass (sodium silicate) onto the material and then exposing to CO2 from dry ice.