If you look at the code for discoverclientrealm.aspx, you'll see that the context object for the page has a member that returns a DataTable containing name/value pairs of the display names and realm URIs of each realm in the system.
If you want to show something different or provide a different UI of some sort, you just need to bind a different list to the UI control (the dropdown) that is used to display the information. If you want, you can store alternate configuration information anywhere you want and read it in at runtime to modify the results.
You'll have to invent a schema to show the "correct" list of realms for each application in your system, but you should be able to figure out which app is which by looking at the wreply query string parameter to get the URL of the target.
I hope that helps.
I'd like it a lot if they had this built in. It isn't in v2 either but would be a nice feature. Lots of people want an HRD list that is trimmed by the target relying party/application.