.............You have absolutely no chance of standing by on any day other than your schedule departure day. There's a reason the fares are more expensive the week you want to go - either that's when everyone else wants to go, or you don't meet the advance purchase requirements for the cheaper fare...........

That is not always true. I have done it many times, check the availability on the web, if there is enough go to the airport and tell the agent at checkin that you want to "go home" a few days early. In most cases they change it without any fees or questions asked, in some cases they will charge you the $100 change fee. The have NEVER charged me the fare difference. I have done this on tickets in many different classes, as I said without issues.

Realize that although you are traveling on a different flight if there is enough space available it doesn't really matter PLUS UAL can sell your seat for the week after again!!