Specifying make flags in rpmrc

[Jay Maynard <jmaynard conmicro cx>]

I've got a dual-processor machine that I use to build RPMs on. When building
the package manually, I give make the -j 4 flag to tell it to run 4 compiles
at once; this makes things go a lot faster. I'd like to have rpm use that
flag as well when calling make, but haven't figured out from any of the docs
I've seen online how to do it. Is there a way? I don't want to have the flag
in the specfile for obvious reasons...