[imp] Custom login with Custom Path and Mode dropdown

[Matt]

I was already using a custom login and logout on a seperate path, like:

$conf['auth']['alternate_login'] = '/path/to/login';
$conf['auth']['redirect_on_logout'] = '/path/to/logout';


Ok, this works very well.

Now there is the possibility that you can let a user chose what kind of
email version he wants to be redirect to, like IMP, DIMP or MIMP I would
like to have that in my custom login screen too.

So I added the dropdown that is normally in the /imp/login.php but I have
a problem here.

The /imp/login.php posts to /imp/redirect.php. But because I use a custom
login path, I'm not able to post to that redirect.php, it redirects me
back to /path/to/login.

I have tried a several of things to post to, to /login.php (which I
normally did) and to /imp/login.php. But in both cases the Mode is not
recognized and used.

How can I use this type of Mode option using a custom login ?