JAR regs say that you can only take account of 50% of any HW component. That correction is already likely to be incorporated in your company Takeoff Perf procedures - TW must be considered as 150% of reported.
THis doesn't mean that you have to do a correction, more usually that the '10kts Headwind' figures you use have actually been calculated for 5kts headwind, and for with 10kts TW, the figures are calculated with 15kts etc.
I certainly wouldn't use any reported gust factor when calulating my RTOW, so any gust you do experience is a bonus in your favour, the absece of which should not affect your performance calculations.
Gusty conditions and knowing when to 'call' V1/VR can be tricky - use your common sense and exercise good airmanship when operating in these conditions. Making corrections to the speeds without a proscribed procedure for doing so could have all kinds of other ramifications (Vmca, Vmbe, etc) so be very wary of doing so.
Actually ,in your example (being pedantic) your V2 will stay exactly the same, but your current airspeed relative to that V2 will fall - that's called windshear. There are certain techniques which can and should be applied when those circumstances are expected, some prior to takeoff, precisely for the reasons you suggest (e.g. using full rated thrust instead of reduced/derate, not considering all the headwind component as usable when calculating RTOW etc. etc.).