If you're feeling brave, or are comfortable messing around with Insteon...
The command that needs to be sent is pretty simple. command1 = 0x20, command2 = 0x08 (0x09 will turn the LEDs back on.) If you have any means to send custom commands to the FanLinc (e.g. a SmartLinc) you could do it yourself. Note that if the FanLinc is V.41 or higher it will need to be linked as a responder to the device sending the command if it isn't already.
If you don't have any means to send custom commands, but you have a Windows computer with a serial port, you could in principle turn off the ISY, unplug the PLM from the ISY and plug it into the computer instead, and use free software that will let you send a command. E.g. even http://busyrat.com/plmtest/ will let you do it (not sure if it will work with Windows 7 though). If you use that, make sure it's got the right Com port to connect to the PLM, then enter
02 62 XX YY ZZ 0F 20 08
where XX YY ZZ should be replaced with the Insteon address of your FanLinc.
That should do it. Then plug the PLM back into the ISY and turn it back on. Whistle innocently and pretend nothing happened.