Just un-do the pipes and leave it for 10-15 mins go make a cup of tea, or if you plan on never using it again, just punch a hole in the air-con rad, did this on my old civic, worked a treat, and removing saves you about the same weight as another person in your car... so i hear anyway. 
Would be a very small person! 25kgs at most I would guess and that would be everything out! All pipes and second rad.
Or a very very small person.
Rad and pipes 3kgs
Dryer 1.4 kgs
Compressor 8kgs
Pipes 1kg
Total 13.4 kgs
You could lose a bit more by replacing the heater box and matrix with a non air con one but its a real hassle and you could lose a tiny bit more by changing the alternator bracket to a non aircon model one. You should gain some power (very little) by the engine not running another pulley and a bit more if the aircon was switched on. I wouldn't have thought you could ever notice the difference though.
As far as venting the gas to the atmosphere its very naughty so don't do it

You should be able to check if there is gas in the system via the refill ports which have a valve like a tyre valve.
Paul