As mentioned, you can't do much about the head angle; but maybe you can tighten it by up to half a degree.
If there's enough spare metal, you could take a few mm off the bottom of the head tube. Check inside the tube for a machined recess for bearing cups... doubt it'd be feasible for a hiddenset frameset, though.
You can put a size smaller tyre on the front, which should also provide some minimal rolling resistance, aero and acceleration advantage. It makes a lot of sense, given you only have like 40% of your weight on the front.
And purely to get the stem lower, you may also be able to shave a few mm off the top of the head tube. If you have an external cup headset, you may be able to find one with a lower stack height too.