I just had to do this myself.
I started a expedition and sent all the PvP generals to it. Then I started a worthless adventure and sent all my other Generals to it. At this point you can cancel this regular adventure or complete it to have regular generals come back and fill the island spots before you bring back the PvP generals.
Now what I also did was I used decorations to fill any places in the lower left of home island map to keep the PvP Generals from finding a place to land cause there are places they can land that you can not build on or place a camp on yourself. By using decorations you can stop this from happening. I had to send the PvP generals out a second time cause I did not use decorations and some of them found spots to land anyways. But after I used the decorations to fill the gaps they all went into star.
You can buy extra Tutorial Expeditions for 10 fish from the merchant under expedition tab if they do not go to star so you can try again.