One thing you might want to consider is just configuring IMP to have
a pulldown menu to choose which server to use -- IMP happily works
with multiple IMAP servers, and keeps prefs and address books separate
for bob@server1 vs bob@server2.
Take a look at /home/httpd/html/horde/imp/config/defaults.php3
and servers.php3 in the same directory. (Note that defaults.php3 is templated,
so you'll need to make a custom template for it, while servers.php3 isn't
there yet, so you'll have to create one based on servers.php3.dist in the
same directory.)
Cheers,
-Rich