I've used this method before: Spray microfiber with APC, let microfiber rest on gum while you clean something else, give a liberal scrub, and it comes off.. At least that is what worked for me in the past
I usually point it out to my dog and let him get it off....... Jus' Kidding! Actually I use a steamer to get it off. Steam works great at getting things like gum, hard candy, and things like that. Make the job sooooo much easier.