I have the same hate for these shaped handlebar. It's even worst for these aero ones who aren't even close to being round!! You will most likely need custom mount. You could also put electrical tape on the left side of the mount to prevent it from sliding down, but it will not look great.
I was able to secure my computer mount on my new gravel bike by adding a layer of rubber tape between the bars and the mount clamp. It seems to be holding. Will see after a few rides if it slides down towards the drops or not.