[Kamog]

I have had success in getting the AI to accept stuff by using trades. Say I have a damaged ship stranded far away that I don't want to pay maintenance on, and it's not worth sending out a repair ship. So I try to gift it to an AI and they refuse. No problem. Propose a trade, and give the ship along with 20000 minerals, and ask for 10000 minerals in return. The AI always seems to accept. Of course, you lose some resources by doing this, so it only makes sense if you have an excess.

So maybe you can get the AI to accept the sphere world by trading the sphere world + 20000 resources and ask for 10000 resources back.