Few fonts will render this nicely; the dashes are unlikely to join. Also if it does break at the soft hyphen, you’ve got an extraneous hyphen added on the first line.

If I were doing that, I’d probably use a zero-width space instead of a soft hyphen. Same break opportunity, removes the extraneous undesirable hyphen if it breaks, but introduces a new word boundary so that wordwise selection can now split your wonky dash. Therefore I suggest <span style=user-select:all>–&ZeroWidthSpace;–</span> because if you’re going to do something ridiculous you might as well embrace the ridiculosity.