You generally need a lot of power and speed in order to get a ankle dm.
There are generally two ways to get an ankle dm on uke (with a kick), which would be a very precise strike to either the side or back of his foot, or you smash the foot into something.
The thing is when you are going for the ankle dm from the front its really difficult to get so much power into such a small area without hitting anything else. Since the feet are at such an obscure place its hard to dm them with strikes. That's generally because you get to the feet so much quicker and in that time you usually don't have enough power to break em.
by all means you can try though