Multi DB Plugin: Unclear installation instruction

There is a part of the multidb installation instructions that contains this:

"One final step is to make sure you have assigned a username and password to be associated with each database. This could be the same as your username and password for the original WordPress database. It's up to you, just make sure that there IS a username and password associated with each one and note what it is. You'll need this information for the next step."

I am using 256 databases. Am I supposed to set the username and password for each one? How can I set one username and password somewhere and use it for all databases (which would be a really time saving option)?