Upvoting as good idea, but most routers I know, evening running custom firmware, don't support delegating a wan prefix on request from lan side.
(But it should be a very early thing to try, if it's available everything else becomes much easier.)
I've tried to set up PD but it didn't work, so I've moved on with other options. Now, after you mentioned that, this feels like a good excuse to delve into what exactly didn't work back then.
(This isn't about ISP-provided locked-down routers either, though those are an abomination too IMHO. Regardless of whether the "last" ISP-controlled device is a plastic router in your home or an aggregator somewhere else, it needs to support and offer PD for you...)