Dr. Dyper

I'm stuck at the part with Dr. Dyper. I already went to the guy in Hotel Cosmopolitan and got the bottle, but every dialogue option with the "Dr." (skeleton on the wall) goes nowhere and no other NPCs will help me. Where do I go from here? Any hints will be greatly appreciated. (Love, love, LOVE this whole franchise BTW. It's rare I see games of such genius anymore!)