I've just been baking a sifted whole wheat miche (70% hydration) with excellent gluten development and fairly short proofing times (4 hours bulk, 1 hour after shaping)...but I can't for the life of me understand how you are supposed to slash this dough.  As soon as I turned out the boule onto a baking sheet to transfer to the oven, the dough flattened out considerably.  

Plenty of oven spring prevented it from looking like a complete pancake but I'm still puzzled how it would be at all possible to slash this loaf - and if so - when and how should I do it?

I've seen pictures here of 82% hydration slashed loaves and I can't figure out how you'd do that?  It's simply not possible as far as I can tell.  There was no way I had time to slash the loaf after it started flattening...literally I had about 10 seconds to get it from the baking sheet to the oven.

Please can someone tell me how to defy physics!

Thanks

FP