Merging CS3 and CS4 pcd.db files when upgrading to CS4 – necessary/possible?

So I'm working on repackaging all the different CS4 Design, Web and Master Collection installs with Composer 7 to do a mass upgrade of all of my Mac users and to integrate into my build train. The stipulation is that existing CS3 users need to retain use of their current CS3 install while the transition to CS4 is made. I know from past experiences that the dreaded PCD licensing data that goes with their various products and suites tramples all over each other, requiring post-install manual updating of licenses -- not at all the automated deployment I am looking for. Now I know that the pcd.db and cache.db are fairly basic sqlite3 DBs and since we use one single volume key the hacker in me wondered whether I could safely merge the old CS3-specific DB with the new CS4-specific one and end up with one pcd.db/cache.db file that would play nice with both. I have to read up on the cache.db file a bit more, it could very well be auto-generated from the main pcd.db file if it's missing so it may just be the merging of two pcd.db files that I am looking at -- if possible at all. Granted, it may not even be necessary to worry about the PCD data and CS3 may just keep on trucking based on what it finds in the CS4 pcd.db file. I will have to do a trial install of one of my CS4 packages on top of a standard CS3 package and see what happens. Short of this though, has anyone attempted something as described above or should I take the long way and install both CS3 and CS4 and then package up just CS4 using Composer 7's preinstalled software method to be sure? Any opinions or experiences with the CS3 -> CS4 process would be appreciated. Thanks, Pepijn.