Normally we talk about adding half the gust factor on the approach
That's why you bleed the headwind/gust factor off over the threshold.
This sort of consideration generally is the province of the heavy metal brigade.
.. in which case, the story is
(a) half the steady wind and all the gust to a suitable maximum (20kts or so)
(b) bleed off the steady wind additive but maintain the gust additive
Reason for the difference is
(a) steady wind has a reasonably predictable reduction near the ground
(b) gust is totally random.
A variety of discussions in Tech Log, eg,
http://www.pprune.org/tech-log/10456...ment-vref.html