There are all sorts of suction cups available on Ebay- - - -(dent pullers, etc.)try finding some about the right diameter and gluing them to the inside of the existing cups with 3M trim cement (gorilla snot). Can't lose much- - - -they're useless "as is".
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!