Use strips of newspaper and wallpaper glue.
About three strips lengthwise out of a newspaper page. Plaster them on crossing until none of the ballon is visible anymore. Put on more layers to make it as firm as you will.
By the way you can also try the same with coloured transparent paper. You glue strips or coin-sized pieces. Leave a circle free on one side.
After drying you remove the ballon. The paper will wrinkle, but you can un-wrinkle it.
Place a small waxine light at the bottom. Very pretty!!!!