That's bizarre. I've never seen a flat tip like that. I'm rather sure it's a manufacturing mistake. The CM-6 plugs have a flat top, but they have a receiver groove in the flat top.

There are two types of the normal top connector. Some are made as part of the plug, and some are the same size and shape connector, but the connector itself screws onto a stud that comes out of the plug. If you have one of those lying around, maybe you could cut the stud off and drill and tap these plugs to accept the stud and screw on terminal. You would have to be very careful how deep you drilled into the plug tip though, so as not to punch through and damage the resistor inside. Probably not worth it for the price of a plug unless you're bored....

AV8TOR