By making some seconds longer than others? Kind of the opposite of precision timekeeping. Changing the size of the unit of measure is a bad idea compared to changing the number of things measured.
If you can get the smear to be gentle enough to not affect your apps, it's a nice workaround for the general problem. There's just so many components running inside a modern infrastructure, and it's hard to get them all to behave correctly during a traditional 61-second-minute leap second transition.
And that 2012 leap second linux kernel bug was pretty epic. AFAIK, people who are smearing didn't experience it.
http://googleblog.blogspot.com/2011/09/time-technology-and-l...
The amount of stuff that still runs an older Linux kernel is insane...
Such precison is well outside the realm of NTP but is not really a problem for PTP. I've worked on Linux systems that have done this; ~100ns synchronization was not uncommmon.
(PTP, incidentally, got it right and specifies that its timescale is based on TAI, so it is continuous.)