Getting to find TKInter headers during build

Thanks to the response to my previous message, I have managed to get
matplotlib to compile, but unfortunately without the TKAgg backend,
because when I attempt to build, I get the following message:

Tkinter: no
             * Tkinter present, but header files are not found.
             * You may need to install development packages

Looking at, this looks like it can't find tk.h in any of
the include directories. But in my win32_static\include folder, I
have got a tk.h. I've tried various locations for the tk headers, but
it still seems to struggle. I even tried setting the basedir setting
in to point directly at my tcl;tk library leftover from my
Python compile.

Anyone got any thoughts - this is the last thing I need before I can
actually use matplotlib in my application!

Kind regards