when your in a match and your host type this in console:
xblive_privatematch 1
and then you can kick again :L and no this isnt detected by the anticheat.
when your done and have kicked whoever set it to 0 again or otherwise ppl wont be able to join your match so:
xblive_privatematch 0
or a way easier way is to just bind it
bind L "toggle xblive_privatematch 0 1"