We run no MED field as well and the only allowable mercy is contact, tap with a rubber knife, hand or your weapon. NOTE the word tap, just enough that they know they have been mercied along with the attacker saying mercy.
It is really a silent kill, the hit player acknowledges with a nod and nothing else.
And it is a single player you can mercy buddy for bragging rights between you him but if he has a buddy with him you are automatically hit.
We get almost no mercies except for the players new to more tactical days who try to run solo, the occasion scout or observation guy gets mercied but it rare.