The idea here is to OOM the hunter, and keep him completely OOM the entire game. To make the Vipers stick, silence the Druid immediately after you put it up on the Hunter. Your pet will go on the druid, and you'll need to watch his health, because the game depends on him staying alive. I'll assume the Hunter will be putting his pet on your Druid as well. Have your Druid take him behind a pillar, get him down to 60% HP or so in bear or cat, while you LoS the Hunter, or eat his Auto-Shots, and then bring him out to try to burst him down. If the pet dies, and the Hunter is OOM, game over; your Druid can now drink whenever he wants to, and his cannot.

After the Hunter is OOM, start using Viper on his Druid, but keep their Hunter OOM. I'll Viper their Hunter, then Druid, and keep switching off. You must assume that their Hunter has Improved Revive Pet, unless you know he does not. Don't let him drink; you've got to keep DPSing him the entire game while keeping an eye on the Druid. Your Druid should be assisting you in keeping their Druid in combat.

If at any time, you get low on health for any reason, start LoS'ing the Hunter's DPS. You can even Freezing Trap him, as they have no dispel. Your Druid has to be spot on with Abolishes on you, and himself. If he gets low on mana, CC them as well as you can with Clips, Traps, etc to buy time.