Well the only way I can think of is to fit a frame around the bath so that it fits under the lip of the bath.
Leave just enough room for the panel to fit between the frame and the bath at the top then at the bottom rebate the panel and fit some strip magnets.
They can be brought in a length as a roll and cut to size.
Rebate the bottom of the frame to take the opposite strips of magnet.
With the panel cut to just enough height to fit under the bath lip but only high enough to allow you to lift the panel vertically so you can slot it in at an angle then drop it down to slid onto the bottom magnets.
The top should be held firmly as it is trapped between the bath and the frame, the bottom is held tight by the magnets.
Don't have the top fit too tight or you might scratch the panel getting it on and off.