Bill N4QA uses the Gutter And DownSpout on his house as an Antenna, with a tuner mounted at ground level with coax entering the house at the base of the downspout. Click on the images for larger pictures of his installation.
Jake, N0LX, has some nice antennas on display at his site. One of the more interesting ideas he writes about on his site is the idea of using a spiral of wire or ribbon as a counterpoise to a vertical. No room for radials, then perhaps this will work for you. Check out his article on a spiral counterpoise for a vertical antenna.
Here is a link to a homebrew 20M vertical by W4INF, easy enough that an 8 year old can do it. Vertical wire and radials are all 16.5′ long.