Use PHP to give basic-Authentication a nice layout

Hi there,

on a webserver that (for old time sake) uses basic-authentication (401)
to give users a login prompt i now want to present the users with a
nice layout (so not that boring popup basic auth. type).

But: i don't want to change the whole server and it's permissions.

So i'm searching for a way to give a PHP variable to the basic auth.
system... (and not the other way around as the standard
features.http-auth does).

Does anybody have any idea, is this possible? Everybody uses it the
other way around or is using a PHP script with dbase (or so), but this
will take make too much time as we have a lot of users already in the
server.