Can you eliminate cigarette smoke odor between walls?
Getting rid of odor is a difficult task in general, particularly since molecules stick to surfaces and often stick in surfaces.

There's a good reason that "Febreze" works well. It contains a cyclodextrin ring that binds many odor-causing molecules. So the molecules are still there, but bound in a form you can't smell anymore.

(I remember an anecdote that they had to develop special fragrances to work with Febreze, but I can't find that anywhere.)

I suspect spraying paint primer inside the walls could work. This is often used to fix smoke damage from fires.