Hi, a great option is actually the tri-rig sigma system; it's basically a stem that has a slot used to mount a single riser bar that holds their extension bar wind in place. the stem works with a regular round handlebar, so you could technically use it on a road handlebar. It is very expensive, about $950, for the stem, wing, and extensions, but it is really the only other option out there besides the Trek Madone cockpit, which can be purchased as an aftermarket part and should work on other bikes.

I personally use an aluminum handlebar by prime "adeyone," which is aero-shaped but has a wide enough section or round bar in the middle so I can get my stem and clip-on bars installed with space to spare. The handlebar itself is actually able to be complete internally routed and depending on the step you choose you can have completely hidden cables.