If you already have a condition or there are none left in the deck, can you gain an effect--that normally induces a condition--for free?
I believe you are correct - you cannot.  A similar but more common situation that can occur in the game is when you are given the option to become delayed in order to gain a benefit.  "Delayed" does not have a card to represent it, so one cannot run out of them, and in these cases, the benefit only occurs if you do in fact become delayed - you cannot prevent it (such as with the Pocketwatch) and still gain the benefit.  It would stand to reason that other effects that use the phrasing of "you may x to y" follow the same rules.