Fast and long

I'd say if you are thinking of drilling bars or fabricating a custom mount for extensions, then why not buy some bars that are designed for mounting armrests and remove the worry of losing your teeth at some point?

I agree - this is the alternative, I can run a standard stem and bar with clip-ons, exactly as I am on the red Trek TTX. In fact, I could just take the front end off that bike, which would mean I have to find another turbo slave, but I do have a tried and tested solution.

There is still some customisation required: I'd have to find a way to deal with the cable routing, which means making some sort of custom headset spacer top cap that mates the headset spacers supplied with this frame to a standard stem. But that's possible.

Also, going this route looses some of the aero benefits, maybe, but it would mean I could alter the fit much more easily by swapping stems.