This can be done while suicide-boosting Seriously in War Machine. The player going long will be getting curb stomps and must be the host.
1) The opposing player going short ("Short") picks up the grenade, then meets up with the long runner ("Long").
2) Long melees Short with the pistol.
3) Short immediately tags Long.
4) Before the tagging animation completes, and Long regains control, mash X and B alternately with your fingers as fast as possible.
5) Long will melee, downing Short. Long will almost instantly cancel into the curb stomp animation, and may complete it before the grenade explodes, killing both.
If the animation completed, a curb stomp kill will be awarded. If not, the player will only get an execution. This method is not perfect, as I got curb stomps about 1/3 of the time and executions 1/2 the time.
Short should be facing the sandbags when picking up the grenades to lower the risk of Long picking up the smoke grenade due to the X mashing.
When I was doing this, about 1/6 of my attempts ended in only my death, while my partner was left bleeding out. This means you may lose a few kills doing this in a match. However, your partner is NOT at risk of losing kills.
I was able to complete both Curb Appeal and Capital Punishment with this method. This will eliminate the need to spend time in weapons boosting sessions to unlock them.