You're up in the bracket where doing a lot of VO2max intervals is contraindicated. Your fitness is very good and you obviously know how to manage it. That leaves supplements, which do work. Take a look at this: Mountain Might, Altitude Training, High Altitude Training
I have not used their stuff, but it gave me the idea of looking into similar supplements.

For an equivocal review see: http://www.bikeforums.net/18019606-post33.html

I have had good experiences at altitude taking for about a month before an event:
n-acetyl cysteine, 2 X 600mg/day
acetyl L-carnitine, 2 X 500mg/day
alpha lipoic acid, 2 X 250mg/day
sublingual B12, 1 X 500mcg/day

I've also used the sodium phosphate as in Mountain Might in a 4 day loading program with good results:
Race Day Boost - Increase Athletic Performance | Hammer Nutrition

When going up quickly to altitude, I've had good results from over-nighting at altitude before the event.