If CAN setup is too difficult to do use an AUX output with a Dutycycle control for an Axis that you choose, might be
TC Cut Level, Retard, or just the Power reduction level I think will be best. Keep in mind to use the Y-axis first and only when the Yaxis is occupied then the Xaxis. Not sure if its a bug or a feature. The AE86 man says its a feature
Fit a weak pullup (to 5v?) to the AV input of your logger and have the ECU do lowside Dutycycle control.
Or, just get a Motec logger and log the channel and drive the SLM condition from that same channel