Yes, it looks like we can manually paint HDRI, but I think those would be more suitable for studio shots, while I am aiming for outdoor renders. Light probes can be used for both, so they sound like the best approach for this purpose. Today I have spent the afternoon building my own socket to hold a 10" chrome ball on a tripod. This is not a trivial task, and it took me several attempts, but I think I've finally got a working solution involving a wooden block nailed to a section of PVC pipe. LOL
Believe me or not, the wooden block fits perfectly on the tripod's screw mount, and the chrome ball fits firmly on the PVC socket. ^___^
Funny thing I had this old Canon Powershot IS3 camera, but never knew it had a built-in HDRI light probe shooting preset. Who would guess? All I have to do is set the EV (exposure value) range, and then set the timer to 10 seconds, so I can get out of the way before it starts shooting. In this mode, the camera will shoot 3 times, each on a different exposure value within the given interval. The default is from -1 to +1 EV, but I wanted to push the range a bit wider, so I set it to -2 to +2 EV. This way, the shots will be in EV -2, 0, and +2.
Once the chrome ball has been shot, we combine the 3 exposures in Photoshop, and then unwrap the probe into a regular HDRI map. The resulting map is twice as wide as it is tall, so I loose resolution by half, which is a sad side-effect. This means the original 2K light probes get reduced down to 1K HDRI maps with 2K widths.
It took me so long to come up with usable chrome ball socket for the tripod that it was already dusk when I started shooting indoors, so the light probes came out noisy. I did some test renders with them, and looks like they are quite usable nonetheless. On the Superfly renders below, the left side is with just a spotlight, and the right side I have added my home-brewed HDRI map (from my kitchen!) in Poser. Dawn is the only thing on the scene.
The differences can be seen on the PBR glass and metals that now have something to reflect. Without that the metals turn black even in Superfly.