At my company, the maximum vacation is 3 weeks for everyone but executives. Therefore I cannot even start negotiating for an increase to 4 weeks.. it's a non-starter because it's "against policy"... even though I think my experience and value to the company warrant it, and I've gotten 4 weeks at previous jobs. (I know I could have made a "hard stand" before taking this job, but that's water under the bridge)

Any advice? I was kind of thinking of taking the "you want to be competitive" tack to get them to change their policy but I don't know where to find the kind of data I would need to support that.