. . .put something fairly rigid, like a screwdriver shaft, in between the center of the clip and the cap, gently make sure the clip is wedged firmly up as far as it will go (so that the ball isn't touching the cap) and then use your fingers to bend the clip back down. When you remove the screwdriver or whatever else you're using for a wedge the clip should be firmly in place. You're permanently distorting the shape of the clip, though, so be careful and standard disclaimers apply
.
Jack