The Crystal Fellows is a single bolt and non slotted clamp If I remember correctly. I have the same problem with Swallow all the way back on a Kalloy knock off. I think without the grooves/slots we are fighting a loosing battle. The only thing i can think of trying, but haven't yet, is some carbon/friction assembly paste. If that doesn't work I am going for a Velo Orange Grand Cru. It looks elegant, has two bolts and a whopping 30mm set back.