A needle and alcohol, bro. (Some for you..... some for the needle). Gotta do it the old-fashioned way, I'm afraid. Needle swabbed with alcohol and poke at the surrounding skin until you can see enough to grab the sliver with the tweezers. Not a pleasant process but look at it this way..... you haven't felt anything until you step full-foot on a sea urchin. The spines on those damn things are totally barbed, and don't come out just like that. Did that once while skin diving and negotiating some very shallow coral reefs many years ago. Had my heel full of the damn things. But I diverted. It's your thumb and copper slivers, right. Needle and alcohol.