Repairing Hormann Door with broken torsion springs

[SFAM]

The last time my Hormann garage door closed there was a large popping sound and from that point onwards the door refuses to open - the control unit reports the error message 5: remove obstruction etc.

I could not see any obvious obstructions so I tried once more anyway and now the door is stuck half way open. I then examined the door more carefully and found

1. The right hand torsion spring has snapped in two
2. The left hand torsion spring is misshapen and "wobbly"

I am assuming that both springs are damaged and are no longer under tension. The very first thing I need to do is to close that door somehow. Here is what I am planning to do

1. Double check that the springs are not under tension
2. Put two sets of of C clamps - one a few inches below the other - on the door guide rails so it does not slide down with a bang
3. Undo the bolts attaching the pulley cables to the bottom of the door
4. Slowly guide the door down by removing the upper clamps and letting it settle on the lower clamps
5. Repeat till I get the door to its resting position
6. Secure the door so it cannot be opened from the outside by placing C-clamps on the rails from the inside
7. Buy and replace the torsion springs etc

Before I embark on this I thought I would ask here - does this sound like a reasonable, and safe, way to do things? I'd much appreciate any advice.