We are currently testing backup beacon features in our software, but it is not yet released.
However, with a bit of creativity it is possible to generate a beacon based on a math channel.
The trick is to create an alarm that triggers when you want a beacon. You can then create a math channel that drives this alarm based on whatever conditions you want. Lap distance, GPS coordinates... etc.
Bear in mind though that alarms as standard only run at 10Hz, which does not allow for very accurate timing. If your FreeCPU is high, you could run the Alarms node up to 100Hz to get more precision.