Best way to clean a Blu-ray disc?

[calmblueocean81]

Sorry for bumping an old thread, but I didn't want to create a similar new one unnecessarily.
I recently bought a boxset (digipack) and every single disc was stuck inside the cardboard sleeve with glue that had obviously seeped down from the edges of the packaging. The sticky substance is on the print/picture side of each disc (thankfully), but just wondering what people would recommend to get rid of the glue? I don't want to use anything too harsh. None of the discs are too bad, but I'm paranoid about it gumming up the works inside the player!

Any suggestions would be welcome!