I have a bit of a problem, I currently use the Bontrager XXX Integrated Factory Overstock Road Handlebar/Stem and it has a flared stem which prevents the attachment of regular lights, GPS mounts, etc. Does anyone know of a clip on aero bar solution that could clip onto this?

probably need to put different bars & stem on, then, get aluminum, ones not carbon..
because you want to clamp on the Aero bars ..

& not too light because they would have to use a quite thin wall tube to shave grams..







....

If it is the same as what is on my Madone there are 1 threaded hole underneath in the centre near the front?
That takes a Bontrager "GoPro" style adapter which then takes subsequent Bontrger adapters for Garmin, lights etc.

I believe you're referring to the blender adapter, which does exist and I do use for my Garmin, however I do not believe aero bars can be attached to it.

https://www.controltechbikes.com/products/item/383.html

?

Claims to mount to a round or square profile stem depending on what you choose.

Wow, I like this quite a lot, the integrated stem on my handlebars are still flared, but this does claim to be designed for these types of purposes. I'll probably reach out to the company and see, thank you!

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.