Different login pages for different virtual domains?

[Lloyd Zusman]

I'm happily running IMP 3.1 for all the email users that I host.

These users access IMP via several different virtual domains, all of
whose URL's point to the same Horde/IMP/Turba installation.  This works
fine.

However, what I'd like to do is this: some (but not all!) of my virtual
domains need to have a domain-specific login page that comes up for IMP.
But once logged in to IMP, I'd like all users, no matter what domain
they logged in from, to be accessing the same Horde/IMP/Turba code base.

Here's a summary of what I want:

 mail.virt-domain-1.com  --  standard IMP login page
 mail.virt-domain-2.com  --  standard IMP login page
 mail.virt-domain-3.com  --  standard IMP login page

 mail.virt-domain-4.com  --  special IMP login page for virt-domain-4.com
 mail.virt-domain-5.com  --  special IMP login page for virt-domain-5.com

What is the recommended way of doing this?

Thanks in advance.

-- 
 Lloyd Zusman
 ljz@asfast.com