A few years back, I had just lost my gold status. I was flying one day from SFO to DFW, and they cancelled the flight (a wide-body). They had one person working the counter to re-book everyone. I ended up getting a taxi to SJO, and got home almost 10 hours late.

I emailed a complaint, and someone called me back. She offered me 4 upgrades. I told her I couldn't use them, since I wasn't gold anymore. She offered to sign me up for a challenge (I hadn't heard of it before then). When we told me I needed 5000 miles (yes, it was miles back then) in three months, I said, "I've done that many miles in the past 5 weeks." After she confirmed that, she said she'd backdate the challenge, and I'd get gold status when the computers updated that night.

So, long story short, it can be done, but only if the CSR owes you something.