[ubuntu] how do I compile a kernel with acpi_cpufreq as a module?

I would like to add the phc-intel module to my kernel so I can undervolt my processor. I got the phc-intel module compiled into a .deb package successfully and I installed it. However, to load it, I have to unload acpi by typeing "sudo modprobe -r acpi-cpufreq". When I do this it says I can't unload this because it's built in to the kernel. Okay, fine, so this means I have to rebuild the kernel with acpi-cpufreq as a module.

I'm following the instructions here. I'm at the point where I need to create a config file that specifies that acpi-cpufreq is supposed to be a module. I ran...

chmod a+x debian/scripts/*chmod a+x debian/scripts/misc/*
fakeroot debian/rules clean
fakeroot debian/rules editconfigs

I only edited the i386/config.flavour.generic because I'm using 32 bit. The config editor appears and I go to Power Management and ACPI options -> ACPI (Acvanced Configuration and Power Interface) Support. My question is... Am I in the right place and if I am, which settings do I switch from builtin to module? The processor option seems the likely choice. However, when I change this to module and save the config file I get the following error when the check-config runs...

check-config: /tmp/tmp.SnaxIwOYEp/CONFIGS/i386-config.flavour.generic: loading config
check-config: /home/user/src/ubuntu-raring/debian.master/config/enforce: loading checks
check-config: FAIL: !exists CONFIG_XEN_ACPI_PROCESSOR | value CONFIG_XEN_ACPI_PROCESSOR y
check-config: 46/47 checks passed -- exit 1

So am I changing the wrong setting in the config? Am I on the right track to begin with? Any help would be much appreciated. Thanks.