Cranking up the fan most likely isn't going to help, at least not very much. The problems with those systems involve mechanical cracking of the solder joints under the video chip. Unless you're literally talking about keeping an ice cube on top of said chip so it never rises above the ambient temperature of the underlying PCB those solder joints are going to get stressed every time you turn the system on or off. I doubt measures like slightly increased airflow will do it. (According to the Danish report on the solder cracking in the G4 iBook their conclusion was that it was inevitable unless the system were never turned off.)

When it does fail you could always try fixing it yourself with a tea light. Nothing to lose at that point.

(Additionally, a little bird who may have been in a position to know once told me that on the G3's Apple had actually experimentally determined that the placement of the chip contributed to the problem and that normal handling with the lid open flexed the board enough to encourage the cracks. If it's true then another way to extend your system's life would be to *never pick it up*, but of course this is just hearsay.)