Dynamo Lights

there is a VO mount that works for suernova like that, I have it on my mudguard bolt

Or use one of these if you have a compatible seat clamp...

Seatpost mount supernova e3 looks like attached.
Has a 3.5mm threaded hole drilled in its arm in same plane as the light is orientated. So yes could mount to a seatpost binder bolt (with threaded nut reducing thingy) or a rack or mudguard hole and it would be the right way up.

You could also open unit and remove the arm as ita just bolted on from inside, again an m3.5 fine thread on it.

Super impressed with the supernova e3 fit abd and finish, yeah it's rrp £45 but have spent more then that on battery lights that have died after 3 months commuting.
Packaging a bit overkill though

Had not realised the seatpost and rack mounted e3 have different arrangement of their narrow and wide led.
Rack mounted = narrow led is in the centre.
Seatpost mounted = narrow led is at the top

Edit. I know how to fit dyno lights, do it fairly often for customers, but got to put it out there. Supernova instructions are the best I've ever seen. Literally everything is in there in clear wording and in diagrams. When pubs are open i will buy the supernova folks some beer, good work!

Also they include 3 decent crimp butt connectors incase you wreck 1,nice. Heatshrink included is also of high quality

Bit late, but if you have a brother with a metal workshop it is possible. You can drill a hole in the mudguard bolt and tap it to take the bolt that comes with the light. I'll try to find a pic, I think I posted it on here a while back.

Edit - found a pic