Karel gave a reply on the BIS forum yesterday, stating that this is the format for adding to the Communication menu:
BIS_MENU_GroupCommunication = [
//--- Name, context sensitive
["User menu",false],
//--- Item name, shortcut, -5 (do not change), expression, show, enable
["Not active", [2], "", -5, [["expression", "player setdamage 1"]], "1", "0"],
["Active", [3], "", -5, [["expression", "player setdamage 1"]], "1", "1"]
];
showCommandingMenu "#USER:BIS_MENU_GroupCommunication";
No further explanation than that at present. But this particular example would add options "Not active" and "Active" to a menu "User menu" under the main "Communication" menu.