I had this problem and ended up using the Noctua fan controller.
NA-FC1
For me, it really was the no-hassle solution. I tried the IPMI approach but every 5 minutes, the Supermicro motherboard put the old fan settings back (fans to 100%). With the Noctua, I was able to get practically silent operation and no fan alarms. Best £18 I spent on my server. It's more expensive than the resistor but it you need to turn your fans up for the summer, it takes less than 60 seconds, you can do it with the server switched on and no messing with soldering irons.