I read about this method on another forum and had the best hive experience yet last night!!!
I used to spent SO MUCH TIME ever-so-slightly adjusting the bars and trying to get the bees out of the way. Sometimes I misjudged and heard that sickening crunch. I also tried using my attachment-cutting fillet knife (dull edge) to gently push them down while closing up 1 end at a time. Nothing worked very well.
Then I read about using a topbar-length piece of thick paper, plexiglass or other similar and pushing the entire length down, bees going with it, pushing tight the bars on each side, then sliding the entire length back out. I only remembered once I got to the hive but had a length of cardboard. It worked great!!! Now I only have to worry about crushing them when placing the bar down onto the hive.
Hope this helps