Jacking up front of car in one go on subframe-dangerous?

[Dum-Dum]

Having cut a 306 into pieces I can tell you that the chassis rails both at the front and under the boot floor are f*cking solid. Took as long to do 1 cut through a chassis rail as it did 2 big cuts through a sill. That said personally i wouldn't like to start supporting on them as they are a bit far back and I like to kneel on the slam panel while working on the car so would be worried about how far forward this would bring the balance point.