I wouldn't think so.  A slug is practically as hard as the original hole would have been anyway, so it would still cause as much pull and friction on the fingertips, maybe even more.

  I had a ball with a shorter span on it and noticed that when I used it a lot, the calluses on my fingers would start to go away.  That led me to believe that a stretched span may help develop calluses on the fingertips.

  If the calluses are a problem, you might look into adjusting your span to relieve some of the pressure on the fingertips during delivery and see if you have the same results as me.
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