I squeeze them transversely (if the hole was a rice grain, I’d grab it by the ends and gently squeeze until it turned into a lentil), to open up the tube, then I clean up the opening with a scratch awl or corkscrew end. Or a nail. Pretty much the closest thing that might work. There’s a kind of fit curve between “can I see it from here,” and “I’ll know it when I see it.”
If the cable goes into the cap, I’ll crimp it down with the needlenose pliers. Bike shops have a special tool for it, I think, that puts a nice crease in the cap instead of mashing it willy-nilly and hoping for the best.