smcFanControl can actually do it, the GUI is just set up to prevent you from giving the command. There's some way to access the actual.....whatever it is....that talks to the SMC to adjust fan speeds, and by using that it is possible to set the minimum to whatever you want. I'd advise against doing it though, Apple's fan control schemes are usually set pretty low to begin with. (Lord Steve HATES computer fans, it has been well documented through the years)