There's etc/pmconfig in n9 just like the n900, but modifying it on my stock kernel doesn't seem to do the job alone, I did reboot after modifying, and upon booting the file was still modified, just freq didn't actually reflect the file, maybe in open mode? Would love for ya to try.....
I saw on kernel power 50's I think update list something about removing nokia code for locking(maybe that code blocks the change taking effect), but not sure if its related since kernel powers so choc full of add-ons..