Unity Android Banner Ads? (AdMob)

Im wondering whats the best way to integrate ads into Unity Android, as Unity outputs apk files directly, there seems to be no way to use admobs native java sdk.

Admob doesn't seem to have custom API for me to call..
so I guess I'm left with reversing their sdk and replicating it in Unity/C#?

Before I start doing this, has anyone solved this or have any other recommendations?