I have @deltaassist help me with his while in the air, sadly all too often. I have never had them say no. One time they said "we show your flight is still on time and will be landing in 10 min" umm, yeah, ok but I haven't even left yet, so they just back me up. Back me up is the key phrase to use, I also tell them to make a note in my record that I am going to run for it.