Lighting, Light Fixtures, Ceiling and Exhaust Fans - porch light on lap siding

Hi ~ I want to mount a new porch light fixture but I have wood lap siding that is 6 inches wide and naturally, the mounting base for the fixture is bigger. I found what's called a mounting block by a company called Portfolio/Laurel Lighting but they only offer it for 4 inch lap siding and I cannot google anything about this online. Any suggestions for how I might go about this in a reasonable manner? The mounting block looked like the very simplest solution since it creates a flat vertical surface that, on the underside, conforms to the steps in the siding, but I don't know that I have the ability to create a custom one myself. There's got to be a better way (or a source for these mounting blocks that fit.) Thank you,
Linda

Try this link

http://www.aifittings.com/whnew24.htm

These can be installed either before or after the siding. They should be available at an electrical supply house.

These are made by Arlington Industries - will one of them work on your siding?

http://www.aifittings.com/k_6.htm