My suggestion relied on the bars being hollow, which it seems they're not. Every alloy bar I've had has been completely hollow so I wrongly assumed the carbon ones were as well.
Not completely solid no but I assume they must have some reinforcing / internal sturcutre on high stress areas which prevents a cable being run internally from one side to the other. No need for anything to exit near the stem as long as a cable can run internally from one bar end to the other.
My suggestion relied on the bars being hollow, which it seems they're not. Every alloy bar I've had has been completely hollow so I wrongly assumed the carbon ones were as well.