How do I free the lighthouse keeper from prison? I haven't found a way to get his attention yet ("the prisoner must be sleeping")!
talk to the guard, then look (or use) the lock and talk to the guard again
how about using the "negative" fingerprint on the jail lock? Combining the bottle with the lock just won't do it...
That can be done after talking to the prisoner.
look for something that's malleable.
More explicit hint:
Spoiler
look in the stump on the right side of the net on the beach
I'm bumping this since I'm having the exact same problem. I have the rubbery stuff... now what? I can't use it on the guard, or any of the items I have, I can't use it on the lock either. What now?
Goodness, how silly am I? OKay, I didn't realize you could walk LEFT of the jailhouse *giggles*