Merge multiple chrome portable installations into one

I have a separate installation for office, home and a backup on the usb stick that I use in other computers when necessary. As time goes by the various copies are getting increasingly different as the contents of the history database are going in very different tracks. I've decided to merge them into one ultimately. How do I do it?

The Chrome sync functionality doesn't seem to properly merge all history records and I believe many would have the same annoyance.