This is easily done through the use of the in-game admin panel, which can be opened by pressing
+
simultaneously, so long as you are the host of the game or have been promoted to admin of the game you are in.
Once you've opened the admin tools, click to "enable creative mode tools" and "show all players". This will allow you to build as if you're in creative mode while still in survival, and to easily find and meet up with your boosting partner.
Once you've met up, open the build menu by clicking
and scroll to the right with
until you're on "wheels and weapons". From here you can then place a warhead, disable creative tools in the admin panel, and use the warhead's control panel to blow up you and your partner which should pop the achievement.
Note: My first attempt of selecting "arm" followed by "detonate" to blow up the warhead manually didn't pop the achievement. However arming and then starting the warhead's timer and letting that run down on its own did, so I would recommend trying this method first.