category for local ports

[Rong-En Fan]

Hi,

I'm creating a new category 'local' to store my local ports.
I added VALID_CATEGORIES=local to /etc/make.conf, and 
a Makefile in ports/local/, which lists all subdirs. The only
problem is that I need to add "SUBDIR += local" to ports/Makefile.
I don't want to do this after each update. So, I added the following
to /etc/make.conf:

.if ${.CURDIR:M/usr/ports}
SUBDIR += local
.endif

But it does not work. make index does not include my local ports
in local/. Is it possible to do this in make.conf with some magic?
If not, then I think I have to patch ports/Makefile after each update :(

Thanks,
Rong-En Fan