You can try, but don't get your hopes up. I too am Plat with Lifetime PC membership, but on recent trips to BCN & MAD had no luck getting into any of the clubs while travelling solo on a coach fare. Others have posted that it depends on who is manning the door, so it's always worth a try. You can even bring a copy of the PC page that shows you should be allowed entry, but that didn't work for me in any of the instances.