I suggest lowering TNT down the hole on a fishing line,or maybe standing over the warren shouting:
"Dowhhhh--i`m a gonna get yer yer pessssky vermint!!"
I don`t know how effective this method is,but i seem to remember a a fantastic moustachioed American rabbit hunter did a series of imformative hunting films in the mid 1950/60`s and this was his preferred method of flushing rabbit out of the ground.
Bax