Whatever you do, please DO NOT resort to this as a fix. I tried various methods, and this one might melt those ribbon cables. Take time to open up the PS3, and only heat up the motherboard.
Yes, this work, but only TEMPORARY. My first YLOD I didnt have a heatgun, so I used a hairdryer, with the motherboard in sweater. The PS3 came back to life for 10 days on moderate use. This DOESNT remelt the solder. I used a 2000W hairdryer, and the temperature (yes, i measured it) didnt even reach 220 degrees Celcius.
The reason this work is because it flex out the motherboard and straighten it. The contact points then touches nicely again. However, with time the heat will cause it to warp again.
My view is to only do this to get your data off your HDD, but it shouldnt be regarded as a fix.
Also, the melting point of the plastic casing of the PS3 is below 200 degrees celcius - if you put a towel on it and let it convex,your case might melt with the ribbons inside if you do it too long. For that reason take it apart and only heat up the motherboard.
If you really dont want to spend 9.99 USD on a heatgun, there is a way using your oven. But watch out for the capacitors. This method I can confirm working, gave me 2 months on my second YLOD. But I got a heatgun afterwards (and a second PS3 just in case ).
UPDATE: just wanted to add this little gem for people who will try this without opening the PS3. See what could happen to your casing :- [ame]
https://www.youtube.com/watch?v=pvs5j0hfWfA[/ame]