Question on GIT usage.

I have a kernel GIT tree to hold my developing patches...

I need to build this kernel for 4-5 different processors (c3, p2, p4, p4-smp, etc).

Is there any clever way to have this one git repository keep these other source trees in sync so that I can do incremental builds?

Should I perhaps have a unique git repo for each different build and just pull changes in from my master repo before building?

If there's a simple command to set up slave repositories like this, please point me to it.

Thanks! Ben