Seige...
A seige, of course, implies beseiging forces. This will become a submarine magnet.
If the carriers are kept in the area, it's a chance for a sub to get lucky and sink (or with American torpedoes, damage or hit with a dud) a flat-top. For that mater, enough atacks, successful or not, and the admirals will be very worried about the sub threat.
If the carriers are NOT kept in the area on a regular basis, there's a chance for an American carrier raid to trim down the Japanese surface forces.
B-17's might be able to fly far enough to airdrop supplies onto the island. Is this possible?
If a seige gets going, the possibility of slipping things in and/or out by 4-piper destroyer, or submarine, is also an option.
You have a VERY interesting timeline going!