Eclipse, use a nail that's a little larger than one of the holes, and hammer it through. The leather will close in a little. Be sure to space the hole the same distance as the others. Or if you have a drill and drill bit that fit's one of the holes......
I tried the nail thing before. Um, I accedently nailed the halter to the table. And have yet to get the nail out of the halter, I did get it off the table though.