How to add multiple users to a page's "custom security" settings?

How do I add multiple users at once to the "Custom security..." settings for a page?

Right now, it seems that I have add them one at at time--which is very tedious given a long list of users.

At the very least, it would be helpful to be able to Ctrl-click multiple users to select them from the drop-down list.

Perhaps what we really need is to be able to define "user groups" in pbwiki.

Thanks for any assistance you can provide.

Cheers,

Steven