I've tried to send invites several times. Seems that it can only be done for someone who is in a lobby with you at the same time. Even then... I've sent out all 5 I have allocated and they never seem to stick (maybe those I'm inviting don't accept?!?). Would be happy to send along one of mine for you... but don't think it can be done unless we're lucky enough to be in a lobby together some day...!