I just use my Earlex wet/dry vacuum. Just tape the vacuum pipe near where I am going to cut the water pipe and the vacuum seems to get most of of the water before it makes too much of a mess.
Did this the other day on a live CH pipe for a kick space heater as this was the lowest point in the system and I forgot to include any drain valve. Isolated the heater, removed the push fit tail and valve (vacuum on to get slight water left in heater and pipe), cut the plastic pipe leading to heater tail, vacuum got most water, put finger over end, opened end inserted pipe support, vacuum again got most water, opened end and push fitted on new section upto mark I had already made on pipe (24mm from cut ??). Checked for leaks and reassembled, all done under the kitchen units and without a flood. I did turn off the water to the CH tank to as to at least limit the flood to one tank full if it had really gone wrong !!!