This already happens! I know for sure because I've played my fair share of Tahm support games. Make sure the minion dies within Targon's range (aka spit it toward your ADC, not away from them) and that you have a stack ready. Maybe you used up your last stack on a basic attack lasthit while the minion was still mid-spit? I know I often surprise ADCs with a "present" when they return from base by spitting a low health cannon at them, much as a cat will deposit a dead mouse on your doorstep.