With the new mirc 6.1 try this...
/bk /ban -k $chan $$1 $$?="Reason:"
What this will do is kick the person out of the channel with the reason you specify however if you cancel it shouldn't do anything.
For my own person use for an alias I use:
/kb /ban -ku60 $1 2 $2-
What the above will do is kick the user (address type 2) for a time of 60 seconds... the $2- is the reason you specify.
Hope this helps!