Make a macro that is:
/invite Playername
/uninvite Playername
And click that once. It invites the player and then uninvites them from the party before they accept, so when they click accept nothing happens, but they are flagged as "In Group". If they try and invite anyone, they get a "You are not the leader of the group" message, and if someone else tries to invite them, they get a "Playername is already in a group" message.
Its fixed by relogging, but i had one guy going for an hour... he would keep relogging and then i'd use my macro and he wouldn't be able to join the party or join any other partys.
/invite Playername
/uninvite Playername
And click that once. It invites the player and then uninvites them from the party before they accept, so when they click accept nothing happens, but they are flagged as "In Group". If they try and invite anyone, they get a "You are not the leader of the group" message, and if someone else tries to invite them, they get a "Playername is already in a group" message.
Its fixed by relogging, but i had one guy going for an hour... he would keep relogging and then i'd use my macro and he wouldn't be able to join the party or join any other partys.