I think a humanitarian route would be to lobby for open immigration in existing democracies. For instance, I think we all would have been a lot better off if instead of creating the state of Israel, we offered US citizenship to anyone who needed it after WWII. I’m also a proponent of a modern day open border policy for the US (where I’m a citizen).
1) You allow open immigration.
2) You then allow a democratic vote, including by the new immigrants, to partition the existing state (the essence of self-determination).
which comes back to pretty much my original premise: that the only way for a geographically dispersed population to have self-determination is to be able to move to a single area where they can them democratically vote to have that area become autonomous or sovereign...
Needless to say, the pre-existing population of that area would likely not perceive this process favorably.
The other option I see is to posit that in modern democracies the principle of self-determination is unnecessary. I suspect a number of people in Catalonia and Scotland would disagree...
For geographically dispersed people? Yes, sovereignty is impossible and undesirable as you’d have to take it from the locals wherever you were getting the land from.
For people living under an oppressive regime (or one they view that way), it’s a different story. They are the locals and thus should have a government that fits the local population.
You can’t create sovereignty out of thin air. You have to take it from someone if you’re going to give it to someone else. All the land on this planet has been accounted for for some time now.