I haven't used triggers in a while and have no clue how exactly ACE AI handles the medical. There might be a more robust way which utilizes ACE's own functions more efficiently but the following should work.
If you were to write a function for the whole thing, it could look something like this.
_medic doWatch _activator; // Medic AI turns towards the activator (dunno if doWatch is the best command here.)
_medic playMove "somehealinganimation"; // Run some treating animation on the medic to simulate him doing something
sleep t; // where t is the time of the animation in seconds. Just check this beforehand from animation viewer
[_patient] call ace_medical_treatment_fnc_fullHealLocal; // do the healing just like before
Now this doesn't check e.g. for the distance between the patient and the medic and you still have to figure out a way to set the correct unit as patient. I don't remember if triggers have a simple way to return the unit who activates it (the patient). If not, you'd also have to figure out a way to set that.