I almost always reply with slightly unreasonable salary requirements and/or relocation bonuses. I have no desire to move but if a place would pay me 50% more than I make now and give me a $50k relocation bonus then I'd probably do it.
I do the same thing with local stuff. I'm not really interested in leaving my current position, but if someone's willing to give me a 25% raise then I may be willing to move on, so I reply with:
I'm not actively seeking new employment but would consider anything at $1XXk. If that is within the scope of this job then I would be willing to discuss further. The number is usually about 25% more than I currently make. If everyone did this it may bring salaries up as they wouldn't be able to say they can't find people. They would be turning down people because of pay.