The basic reasons lifters stick, or their valves do, is that either 'gunk' clogs the valves or varnish accumulates on the lifter body, oil feed, or valve.
There are a few tried and true methods of cleaning/correcting these conditions, and I want to convey these, but in our litigation-happy culture, I simply cannot tell you what they are...
OK.. I will

:
You can use a qt. of kerosene in your oil, or any of a number of additives such as SeaFoam, Lucas or Marvel Mystery Oil or you can substitute a qt. of ATF for a qt. of oil.
I do not recommend the first because of kerosene's effect of stripping the oil coating from the internals, creating additional wear while it aids the lifters.
Oil additives have varying formulas and achieve varying results, but no big downside to their use.
ATF has the benefit of first being a lubricant, but unlike motor oil, has a disproportionate amount of detergents in it's formulation, specifically to keep the valves of an auto trans clean, and last a long time in what is essentially a 'closed system'.
This is not a snake oil treatment, it is a tried and true method used by many enthusiasts and mechanics since hydraulic lifters were first introduced by Pierce-Arrow in the 1930's, just search the web and see how many times this is recommended as a cure, albeit not a cure-all.
Any of the additives mentioned above will dissolve varnishes and open restricted valves and oil galleries.
There are a couple of caveats though. It is best to add them to fresh oil and operate the engine for no more than 30 min. (after fully warmed) and not place the engine under extreme loading, though you don't want 30 min. idle time either.
Secondly, immediately change the oil and filter afterward, draining it while still very warm (not HOT) before the gunk can fall out of suspension and varnishes redeposit on the internals.
Then, it would be prudent to do a short service interval of the 'new' oil of say 500 - 1000 mi. to insure that all of the additive and any remaining varnish and gunk is expelled from the motor.
I'm not trying to take the bread from Jake or Charles mouths, and I think it's great that they claim to have produced a superior lifter. But, I've never seen a hydraulic lifter that was immune to the issues suffered by the oem ones (though several may have greater longevity before succumbing). Nor do I believe we have any longterm 'fleet' data on their new device upon which to make absolute claims.
Then there are those who are budget restricted from implementing the flat6 solution and this method will offer them some relief, even if it may not be 'as good', it's still better than doing nothing, at a price many more can afford. And if performed every 25k mi. or so, should at least stave off the worst of it for many more miles than currently experienced.
[disclaimer] Do your research and adopt this fix on your own accord (placed here so that my wife and I may actually get to retire someday... that is unless
HulaBwana finds another way of taking it away from us...

)