I used a similar method once on a Renault where there was absolutely no room for spring compressors, cutting the old one out was easy (I used the hot spanner)(oxy) then used ordinary spring compressors to shorten the new spring before wrapping loads of nylon webbing around it and getting it into the gap as quickly as possible. I treated it like a live bomb, Im sure it would have taken my head off if it let go.
The problem with this sort of technique is that if anything does go wrong you have huge amounts of strored energy and no way of controlling it. If you drop an uncompressed spring it will fly off in any direction, now add say, 1 ton of stored energy and think of the damage it could do to bodies, the workshop, the car etc.
Another problem with modern springs is that most of them are rising rate, ie the outer turns need less force to compress them than the inner turns. When you apply spring compressors you cant clip onto the outer coils because of reduced access, you tighten the compressors until the centre coils are closed up completely but the outer coils just expand to fill the gap and the spring still wont come out.