I was successful with both advanced Silver and Gold status this year. I had been a UA flyer for years, took last year off, and started from scratch this year on CO.
Silver: Once I had around 18k EQMs earlier this year and a booked flight that would carry me over the 25k EQM mark, I called the OPSC. I explained that I already have my 25k flight booked and would really appreciate getting Silver status TEMPORARILY. The rep put me on hold for a minute and came back saying that she'll give me silver until June 30th and I have until then to earn it fully. This was around May and my flight was in June.
Gold: I reached around 42.xK EQMs and decided to make a MR for gold. I booked the ticket for early November and again called the OPSC. The rep told me that she can't do that but that a supervisor may be able to. I talked to the supervisor, who looked at my booked flight and half jokingly asked if I was doing that flight for status. I said yes and that I would really appreciate temporary gold status for that flight. She put me on hold for a couple of minutes and came back saying that she set it up so that I have temporary gold through the middle of November (2 weeks out from the call). She closed with "we appreciate your loyalty" or some variation of that.

disclaimer: I didn't think of this myself, I read the advanced silver status on a post on flyertalk in Dec 2005 and figured I would try myself and once gold came around, there wasn't any reason to ask for that.