Tranfer photos that came from iTunes into iCloud

Occasionally I get handed a iPad/iPhone which has a photo collection on it that was sent to the Photos App via a cable from iTunes. You remember, how we used to do it in the old days when the world was in black and white.

Naturally, I want to switch that device out of that mode and into iCloud Photos so that all the old photos and any new ones are backed up and replicated between the devices. If you have ever done that you will know that the iPad says it will delete the photos that were sent from iTunes when you switch mode (potentially thousands of the things).

I have an example I'm working on right now. There is a photo collection that only exists on the iPad. The computer that sent those pictures from iTunes was retired years ago.

What I want is iOS to be changed to just shut up and upload the photos instead of deleting them. What I actually have is us manually selecting the photos one at a time and sending an airdrop to another iOS device (one that has iCloud Photos switched on) in batches.

I understand I'm not going to get an iOS fix any time soon (if at all), but does anyone know of a better way to do this? Perhaps an app that can do the transfer? I'm finding it difficult to search for something to do this, as I can't find the right combination of words to search for.