Yeah I would suggest something metal to plug the hole that you can still get out instead of silicone, just use a little petroleum jelly. I had 2 cones so I plugged on and still have the other open.
I ran the shaft of a qtip inside of it and put a dab of silicone on each end (let dry). You could prob get a similar effect from just putting in a small nail 1/2 inch with a wide head. Many different options.