wp-admin as subdomain address and multisite login from one place

I've been doing a fair bit of research on this idea, but as yet, haven't come up with a working solution.

I have a multisite, running Pro Sites and Domain Mapping (among other WPMU DEV plugins) - I charge people to create blogs, in similar vein to edublogs (since that is what the plugins were created for). I'm quite keen to make things as white label a possible, so I use an admin theme (called clientside since I really like it), and most importantly, a plugin called "Hide my WP" which has various settings allowing you to hide any hints of wordpress from users - OK, so that's my setup.

What I'd really like to do is have one place where users login and are taken to their dashboard. Moreover, I'd really like to change sitename.com/wp-admin to a subdomain, like dashboard.sitename.com - when they login here, they are taken to their dashboard.

Here's my questions:
1) Is it possible, using domain mapping plugin, to allow users to login at the main site and it takes them to their dashboard?

2) Is there a way to either move wp-adin to a subdomain, or in some way alias it so it looks neater?

Thanks in advance or the replies.
Sam