I have a little more space but the same neighborhood concerns you do, dcarch. Going to see if
these wooden tomato cages (scroll down for photo) tested at the U.C. Bay Area Research and Extension Center facility will serve as cold frames for a few weeks. Plan on wrapping plastic a few feet high around the 4 eight foot 2x2's, then poking the side and end supporting dowels through the plastic as needed The roof will be angled by inserting dowels at different levels. To fit in with the neigborhood homes, the cages will be painted white. Should be elegant. I hope.
Have no idea if this will work. Don't take my advice as this is my first serious tomato garden (serious in intent, we'll see how serious the crop is). Perhaps the plants won't have enough circulation in the two and a half by four foot area I intend to surround by the cage; perhaps I shouldn't be planting in the ground at all here in April.
If this sounds like a bad idea to anyone, I would appreciate a heads up . . .