I'm not experienced with A. tigrinas/zebrinas but I've waited for dormancy on other Elephant Ear varieties. I'm guessing you want to force dormancy because you want to store it as a bulb until spring. For outdoor Alocasias and Colocasias in colder states, the general rule is to wait until they have gone through the first fall frost. Then you can choose whether to: (a) cut it back so it has more room to grow smaller & slower in a sunny indoor spot for the winter or (b) prepare it as a bulb. I've done 'a' with success in my first year of trying. Haven't tried 'b' yet. Wait and see if someone else on here has experience doing this with your variety. Or post in another discussion and see if you get more responses.

I dont see that possible on a heated porch, they need cool temps, a picture would help. I love the cooler temps,but I hate having to watch my plants take their winter nap..