Island Hopper is not the only way to get HNL -GUM. There's also a non-stop.

If everything runs on time you could go straight through from SFO with minimal connect time.

I'd suggest buying a roundtrip from GUM-ROR though, especially if you're bringing dive gear. It's often weight restricted and I think that'll be the most tricky part of your journey - it's not a destination that's served everyday and you could get stuck.

I priced it out for January and you're looking at around $550 round trip from Guam. If you can non-rev the other segments it would still be a very cheap Palau vacation, air travel wise. You could always price it out the day of travel and if you don't make it out to GUM just cancel, as it'll be within 24 hours.