I have bled them down using a home made fixture to hold them in an arbor press. In my case it was easy to do because I have a stress gauge so I set them up at 500lbs and just let them sit for awhile. Then I would just watch the gauge and when it stopped dropping that's when they are empty.
You'll have to do it 2x to get it all out because when you release the press a little bit might suck back in. It's not much, but when you are trying to set clearance to .020 or so then you need to be accurate. Also, make sure that the galleys are empty before putting them back in the motor because those suckers will actually draw oil out of the galley if there is any in there.
You can do it in a bench vise also, but it's not as fun.