Recently, my mom has a problem with her ears and we were swimming together the other day when I noticed a silicon-thingee stuck on her ears. Upon asking, she told me it was new silicon earplugs that fit your ears by molding itself.
Well, that got me the idea that you can actually use these silicon earplugs as mold for your earbuds. Not only will you get a perfect mold for your ears, essentially your earbuds will have customized earbuds without paying for an expensive, custom earbuds.
Besides that, if you lose the earbuds (the rubber part I mean), these would make great replacements.