I just read the OP and bypassed the rest of the discussion.
I used this strategy, sort of, to get my scholarship increased at what would ultimately become my alma mater. I sent the admissions office an e-mail toward the end of the cycle and told them that I loved the school and would love to come there but that the cost was a deal-breaker for me and that that was the only reservation that I had about attending. I was very frank with them about my situation, told them that I had the ability to attend a well-reputed institution for almost zero cost and that, while that school was not my preference, the financial consequences of choosing a school were high-priority for me.
A couple of days later, I got an e-mail back saying that my scholarship was increased; this increase ultimately ended up being worth $60-80k over the 4 years. I have no idea if this is common or not, but there's at least one case of this "strategy" working.
I should add that everything I said in my e-mail was true and genuine - I wasn't trying to play a "game," and it certainly wasn't a situation where I would still attend that school even if the response was no. If you can do this tactfully, then I don't think there's any wrong in asking - the worst thing that can happen is they say no. But sending something along the lines of, "sup bro, I'm basically one of the best applicants there is, I need more money to come here" is probably not going to get you a positive response.