Forget about the leptin component.
Nicotine (ass well as simple sugars / carbs) directly effect the brains output of serotonin (sp). What this means is when you inhale that smoke, the nicotine will spike serotonin which is the brains "feel good juice". this spiking of serotonin causes us to feel better, to be more at ease and lastly (maybe most important) it brunts and or severly deminishes the hunger or feelings that come on us that we must eat to feel better.
Have you ever noticed that depressed people (or maybe when you are feeling blue) crave sweets, your serotonin may be low and the brains calls on substances that will cause a spike, i.e we grab for chocolate, ice cream or some other sweet which will cause serotonin to spike to comfort levels (very similar to a smoker after a flight - they need that serotonin spike 1st thing after landing to get them back to comfortable norms).
Man i'm long winded
in closing, while you diet, you do away with some of the very things that your body may crave because it's accustomed to elevated serotonin levels from sweets,etc.
Nicotine can cause that very same spike your body craves, think of it like whenever you give yourself a nicotine dose, you essentially gave yourself a sweet snack (like a Snickers bar). the nicotine spikes serotonin which sauses a nice satiated feeling and presto your previous huger pains have vanished.
How to do it correctly (if there is a way) and a smallest crunch to wallet.
Purchase the 21mg nicotine patches (14 count - two weeks - nicorett clear patches) and cut each patch in half (as needed)which will give you enough for 4 weeks at 10.5mg per patch. you can probably avoid nicotine addiction by cycling two days on / two days off meaning that one box will last eight weeks.
Hope this helps