rpmbuild and kernel src

[xyzzy at hotpop.com]

Is there a command line way to invoke rpmbuild on a kernel src rpm for i686 
and not have it build the "up" rpms?

I tried to use --define "buildup 0", but that didn't work...

The only way I can see that works for me is to modify the spec file to have:

%ifarch i686
%define buildup 0
%endif

... after the check for all_x86.

This is not clean at all.

In other words, is there any way at all to override spec defined macros from 
the command line?  That way, the above would work and also, I could redefine 
rhbsys to do something meaningful without having to modify the spec file.