I really haven't *understood* kernel configutarion but i can tell you what i do when i want to add a config option. I first edit arch/i386/config.in and add a line that looks like
bool 'whatever explanation' CONFIG_WHATEVER default
this is supposed to mean that CONFIG_WHATEVER is a boolean taking values y or n. When you 'make config' you'll get something like
'whatever explanation (CONFIG_WHATEVER) [default]'
and you type in y or n. Now this automagically #defines CONFIG_WHATEVER in <linux/autoconf.h>. Code that is specefic to the configuration can now be enclosed in #ifdef CONFIG_WHATEVER ... #endif so it will be compiled in only when configured. If you want any more explanation than can be given on one line, you can have a set of 'comment ...." lines before the 'bool ....' line and that will be displayed for you during configuration.
I don't know if you'll find it useful but still .....
Venkatesha Murthy (email@example.com)