It is an interesting question. A while back, someone joined this forum saying they were a hotel front desk clerk. They said that you are more likely to get an upgrade if you slipped the clerk some money. They didn't last here very long, of course, since they were saying some things that employees just shouldn't say.
You can try sending a really nice email as well as a really nice fax as well as talk really sweetly to someone who is a room controller, before you go.