if there are 16 or less units (that total 960 or less men) in multiple stacks in a province that I want to bribe. I send one crap unit there first to attack it. This causes all the stacks to merge into one, and allows me to bribe them all together.

I still haven't figured out what will trigger losing buildings and what won't though. Sometimes when I bribe, I get all the buildings intact. Sometimes many are still detroyed in the changeover, even though no battle took place. Any ideas on how to guarantee a "peaceful" takeover that won't result in the loss of any buildings?