krylon sells clear gloss and clear matt spray finish in spray paint cans. its acrylic resin based and i would think an excellent sealer for bamboo. the clear matt might not look as 'plastic' as the gloss. basically its acrylic resin (same used in acrylic aquariums) dissolved in solvents. it might be a good alternative to the urethane but give it a day to cure and then soak it to remove any residual solvents.