that removing the phillips #1 or #2 screw at the front of the shock and pressing in on it --maybe rapping on it with a mallett to help it along--- will collapse it fully.
Then reinsert and retighten the screw.
You can also drive up close against a wall, turn the car off, set your parking brake and put it in gear, remove the screw and then put your jack against the wall, and screw it up to collapse the strut fully.
Either way, once the bumper is off, access to the screw is easy.
No drilling is required. No fluids come out, either.
But if you drill a hole in the bottom, gas a fluids come out.
yes be careful if you drill.. stuff squirts out all over..
my screws were shot.. so i got mad and broke out the hack saw and started cutting.. and i hear psssssssssssssst.. i said,"wonderful, all the air is out" then i hit it with a hammer and,,, darn i got nailed in the head and ear with fluid that smelled like sweaty socks.
For the record, one of my rear bumper shocks, the passenger side, wouldn't collapse significantly until I drilled a hole in the oil bladder and allowed it to sit overnight. The next day, I could compress it without much effort.
However, all four shocks refused to collapse unless I first drilled through the screw hole after releasing the pressurized gas(N2?), in order to release the pressurized oil.
This was on my 76 280z, maybe others are different, but collapsing the shocks w/out releasing the oil was like trying to compress a strong coil spring.
Messy job but looks much smoother with the pushed in bumpers.