hmmm
I think it can be done cylinder by cylinder if the cylinder is at TDC, trans in top gear and emergency brake on, cylinder pumped with compressed air to keep the valve closed. TDC gives max clearance on the cam.
The downside might be that if your air supply fails, the valve drops into the cylinder, and you may be in for a bit of work to retrieve it. Maybe a magnet would retrieve the valve in the guide but if not then it's off with his/her head.
I haven't done this myself, but a friend had an '84 M6 on which the stock USA single valve springs were replaced with the euro double springs.
I am considering to do this with my coupe and to that end got a cheapo mcycle compression tester from ebay. I figure to use the spark plug adaptor and hose on that tool, plus my compressor, and some luck, some elbow grease, etc...