Hello,
the doc build process is a lot of hand-crafting work and it also
requires the full source of matplotlib just to get a couple of
directory.
I know that code duplication sucks, but I'd suggest to include
directly into the basemap dir all the files (sphinxext & _static at
the very least) needed for the doc compilation. This would help a lot
the distributions (Debian of course 
).
Thanks for considering,
路路路
--
Sandro Tosi (aka morph, morpheus, matrixhasu)
My website: http://matrixhasu.altervista.org/
Me at Debian: http://wiki.debian.org/SandroTosi