I think the first has to be the certification by the chief of the defence staff that whatever is needed is needed now and within a particular time frame, along with a clear elaboration of why it can't be done with the existing rules, a clear indication of what specific rule is being suspended and for what specific purpose, and a clear indication of how this is going to speed things up.
I think to a very great extent it's case-specific, but you have to start with a clear, unambiguous statement of the chief of the defence staff that, whatever is at issue, it needs to be purchased right now.