I successfully did this in the mid 1990s, just after my senior year track season was over. I was an 800m runner and had just come off a PR of 1:53, at a last chance meet in mid May. A guy that lived down the street from my parents was running in a marathon the first week of June. He tried to get me to run it with him. Him and my dad were giving me all kinds of shit about it, questioning my manhood etc, so finally I agreed to do it. I hadn't gone on a run longer than 10 miles since late April. At the time I was running maybe 30 miles a week at most. I was more of a speed guy than an endurance guy, but I worked hard in the weight room and on hills. Even though I didn't have a mileage base, I think this work helped me. I didn't go into the thing thinking about breaking 3 hours. I was looking to finish and run a respectable time. I started out Trying to hit 6:25 pace and was able to hold it fairly comfortably until 22 miles. I fell apart the last 2 miles bad but still ended up running 2:58. My feet were killing me. I couldn't get on my dress shoes for work the next day because my feet were so swollen, I had to wear my Dads shoes. It took me a couple of weeks to start feeling normal again. I've never run another marathon since. Maybe I would have enjoyed it more had I trained properly.