Use specific IDP based on virtual host

[Josh Brackett]

Our virtual host setup works something like this:

https://{clientId}.{application}.com

So, depending on the URL the user is trying to access our application from we can determine which IDP they should use to attempt a login.

My question: Is there a way to tell the SP "given this URL choose this IDP"? I've read some things about appending an entityId parameter to the URL string but that's not quite what we want.

Thanks
Josh Brackett