CG,
I didn't think you could negotiate that sort of thing in government jobs unless it was advertised at more than one pay grade. For instance, GS-07/09 Target GS09. You might think you are qualified at the higher level, but they might offer the job at the lower level and "promote" you after a specific time period. If that's the case, maybe you could try and talk them into "save pay" during that period, but I wouldn't approach it until I knew at what level they were going to offer the job.
JusPeachy 
