I have xenia really close to the top of my tank, and only once did I need to do a water change big enough to leave them in the open. While the water was siphoning out, I used a medicine dropper to gently squirt them with water to keep them wet. It woked for the xenia...

But I second Jerry's comment - your normal water changes generally wouldn't need to be more than 10%. How often are you doing your water changes?