Edit: I had not considered the point about these lights being flood lights, and I agree that they're not adequate as main front lights.
I was tempted to delete this answer, but I think the direct answer to question on "how to mount odd shaped object to bike?" is valid and there are valid use cases for floodlights in bikes, in my case, for night MTB riding. I'm primarily an MTB cyclist and where I live there are no legal regulations on bike lights. In regard to blinding other road/path users, I'm aware of the type of lights I use and I turn them off or aim them away from other people's faces.
Flood light in the handlebar are recommended, for example in rocky and slow climbs, where you swing the steering repeatedly to keep balance. The flood light pointed down and is used to illuminate the nearest couple of meters ahead, starting from the front wheel contact patch onward. My setup includes a helmet mounted "spotlight" that illuminates further away ant that I can aim where I'm looking at while the handlebar may be pointing in another direction.
Yet another point for MTB use is that you need some upwards lighting in case of a low branch or such, and also, you're not on level ground, so a spotlight may point too high in one part of the trail and too low a few metres after.
The low power of such units actually makes them less likely to blind or dazzle other path users, specially pointed not straight ahead. In complete darkness, after eyes have adapted, even the limited output becomes use-able and does not take the eyes out of "night vision mode" that much.
Also, Indeed flood lights are of little use for high speed riding, neither road or MTB. They do not illuminate far enough to react to any danger.
End of edit
I once made a cell phone mount with some PVC scraps and a hose clamp. The PVC was a bit thicker than 1 mm or about 1/16. I pre cut a shape from a flattened portion of PVC pipe(Imagine a rectangle, about the same size of the phone, to which you add trapezoidal flaps on each side) , then softened it on boiling water and grabbing it with pliers and with kitchen gloves, I wrapped it around the cell phone, making the flaps into small hooks that grabbed the phone. The phone was in a silicon protective sleeve.
Then I made two slits in the flat part of the PVC slat and threaded a hose clamp trough the slits and then tightened it around the handlebar. A strip from old inner tube, rubber hose scraps, foam tape or certain types of handlebar tape can be used line the handlebar to prevent scratches. It also increases friction so you don't need to tighten the clamp too much for the assembly to be stable. I used foamy handlebar tape that had adhesive backing that made it easier to install the clamp.
You could perform a similar approach for the lights, but the hot PVC may deform the light's casing, so you may take a scrap of wood and roughly shape it to similar size of the lights and wrap the PVC around that.
In my case the bracket was permanently attached to the bike, the tabs flexibility allowed me to take the phone in and out with little difficulty, yet it was secure enough to jump down from a curb or ride over a speed bump without letting the phone fall. I used it for urban navigation for a time when I was on delivery.
You can make this bracket out of sheet metal, specially if you can leave the lights permanently on the bracket. You can also make only 3 tabs and closing the fourth side with a protruding bolt, so you can remove the lights when needed.
Instead of hose clamps, you can also use some pipe clamps normally used to secure electrical conduit to walls. They are plenty strong for the small weight of a light and are already shaped to hold on to cylindrical shapes.
You can also simply make a flat backing for the light (Out of wood or metal), with the slits for the clamp and adhere the light to that with double sided mounting tape or epoxy. (if you don't obstruct any functionality with that.)
A third option is a wooden strip ( slightly longer than the lights. Adhere a small wood block as a stopper on either side to prevent the light from sliding off. If made from metal, simply cut a strip longer than the light and bend a little portion on each side to shape it like a square bracket "[". Then use zip ties to attach the light to the strip. You can attach the wooden or metal strip to the bike with more zip ties, hose clamps or pipe clamps.