Here's what I've got. I need to trim to weight off this thing for a 6km hill climb.

Scott Addict R1 52cm
Thomson Masterpiece Post / Stem
SLR 135g seat
Dura-Ace 7800 SRM w/ PV7 (Don't want to change this, but could change rings, or get rid off one ring / FD.
7900 shifters, dérailleurs, and calipers
Speedplay Zero (Steel)
Zipp 202
Vittoria Crono CS
Dura-Ace Cassette
Zipp Skewers
Won't have any bottle cages on.

Looking for ways to trim some weight, but without my wallet floating away. I'm not against ditching parts that won't really be needed (front der, outer chainring etc).

Replace Saddle with Ax Lightness Endurance 74 grams
Replace steel Speedplay axles with Ti axles available on ebay
Replace Zipp Skewers with lighter Tune or KCNC models
Replace seat post with Extralite or Ax Lightness version
Replace Stock Shimano Cables with Aligator or Nokon version
No change needed with Zipp 202 wheels. These should already be less than 1200 grams.

Masterpiece is good but heavy...
Speedplay Alu. bowties and screws.
Token seatpost 120gr.
Throw away compression device - use Gum-Gum or other.
Replace brake booster nuts, hood nuts, DR bolt, rear Dr pivot bolt, stem bolts, seatpost collar or/and bolts, FD bridge and bolts, bottom cable guide bolt, velopugs, Gore-Tex Ultra cables, DA crank Ti bolts.
Get on the diet...

They shift like crap, but for the limited cogs you'll be running in the hill climb, especially if cheap, it might be worth experimenting with a lightweight cassette (test before hand). Seems like you could save a big chunk of weight with one of those for a single race.
Bolt tuning is a nice way to find some grams, but your set up is pretty light and hill race robust right as it is.
Lightweight cables and housing is a solid idea, as mentioned below.
Considered carbon chainrings?

PlanetX brakes will save around 90g (£100)
Their Ti skewers are a bargain at the moment (£17.49!) and are about 44g
I have a SLR 135g(actual155g) seat, bought a damaged ripped one off ebay for less than £5
stripped the cover off and trimmed it a bit, now less than 120g (got the idea from here, here do a search)
perfect for short hill climbs