When he grabs you, put an elbow between him and you at his neck. In fact you can hit him with elbows. Hit the side of his body and don't stop punching till the ref says stop.
Lewis did lean on Tyson a bit, but he also landed some uppercuts on the inside, so leaning and hugging wasn't his main tactic against somebody who tried to fight on the inside.
The key is to wait another 2-3 years until he retires, which is a viable strategy that a number of heavyweights are already implementing.
Povetkin should have lifted his head a few time when he diving in. Go full on with a sumo wrestler type head butt. When Wlad is grabbing out with his octopus arms clasp his arm in an arm bar and dislocate his elbow. That would be less cheating than Wlad carried out.
Povetkin should have stomped on wlad's instep, then kept his foot there and pushed or lifted him up and away - thus stretching and tearing the ligaments in bitchko's foot so bad he couldn't stand up straight for any length of time.....then side stepped him with a left hook, switch to southpaw and knocked him out!!!
It would only take one shot and he wouldn't want Povetkin anywhere near that area. A hard wild backswing with the elbow out towards the head and an uppercut to the "body" would have had Wlad thinking twice about that technique.