See the OI documentation available
here. The LEDs are "echoed" on the PWM connectors. If you can find a beeper that works at 10 milliamps, and that you can hear over the noise at competition, go for it.
If the issue is just not wanting to look away from the field to see the indicator, you might consider a "head-up display", with one or two LEDs mounted to the corner of your operator's safety glasses and wired to a connector on your OI.