Well I would say it depends on what your definition of 'live sand' is. If you are wanting to keep copepods and the like alive, you will need to provide them water and nutrients to survive off of. If you are looking to simply keep certain types of bacteria from dying, you can typically store it for a period of time. Ever see the sealed bags that you typically buy the stuff from the LFS in? Not much goes into keeping that stuff alive, save common sense stuff (no storing at 20 degrees, leaving in the sun, etc.).
That being said, if you are removing your sand that has been in your tank, there will be tons of things in that sand above and beyond simple bacteria that will go with it. Storing that in a garage will inevitably kill it off and should you decide to use the sand again, you will have one hell of an ammonia spike due to the die off. It is compounded even further since you are stirring that stuff up and releasing the toxins into the water when you take it out and put it back. So my opinion is that you technically could store your sand and keep it live, but you would crazy to try and reuse it after it being offline for awhile. I would clean the sand and treat it as dead sand should you decide to use it again. In an estbalished system, or at least one with live rock, it will become live soon enough.