Crank Pulley bolt removal - 1.6 Kent Auto

Hi All,
 
Can I have some tips/suggestions on removing the front crank bolt which holds crank pulley on with motor still in car and car being an Automatic?
 
I've tried a big bar and cranking motor over with coil lead off. Wont budge it, just throws the socket and bar off.
 
Haven't tried a ratchet gun yet as radiator is still fitted and even without looks like I'll struggle for room.
 
Any suggestions as I cant lock it in gear like a manual...
 
Was also thinking a piston stop, but that will most likely bend or break.
 
Thanks,

single hex socket with a long 1/2" breaker bar ,put the breaker handle on the ground (passenger side) and scket on the pulley bolt.with assistance small cranks and it may come loose
or
there is a tool that acts like a rattle gun but is hit with a hammer and impacts the fastener tho im unsure what the tool is called,i used one on a commodore some years ago and worked a treat