I think it should be possible.
Go to ~/.PlayOnLinux/WineVersions and take a look. You will simply see all the already installed versions.
Inside the maps there are a few files, I think they are representing the files a usual wine-installation puts up on your computer. Try to copy all the files from your system and put them in a new map called bleeding-edge or whatever (or even better, just make syslinks to them, so they will update when you install a new version a few days later). If you look at one of the existing folders you'll understand how it should be, ~/.PlayOnLinux/WineVersions/bleeding-edge/usr/ is the same as /usr/, ~/.PlayOnLinux/WineVersions/bleeding-edge/usr/bin is the same as /usr/bin/ etc.
I have not tried to run an application like this, but I could see that PlayOnLinux recognized the new version.
(I have not looked at the source, and all this is just smart guesses..)
I think PlayOnLinux will work on 64bit-systems too, since it is written in Python. ^^
And I am pretty sure that most Wine-users use the 32bit-version, even if they are on a 64bit-platform.