Executive ghettos are NO fun when it comes to neighbors. First, I'd speak to the people on either side of you and see if they'll be cool with it in the yard for a set period of time like a month. If the people most involved are good, then you may be able to get away with it. If you have an in ground pool, make it look like a pool house.
You'd probably have to screen it with hedges, etc. to hide it from plain view.
OTOH, in this economic market, odds are you'd be able to find warehouse space with a commercial garage door (14' high) and rent it for utilities + a couple of hundred a month on a short term lease.
One cannot overestimate the benefits of working under a roof especially when polishing - no glare to reflect back and burn you, or 100 degree temperatures to make the sweat droplets mark up the newly shined surfaces.
Good luck and happy polishing.
Today is a gift, that's why they call it the present.