Hello,
At the moment, the way the suspend system works, is all suspended domains point to a Directory. Having a per-suspended-user might get a bit messy in terms of keeping track of each suspended page to ensure it's there for that User, with the text you want it to show.
However, the current system, you can use an index.php instead of index.html.
In the index.php, have checks for the $_SERVER['HTTP_HOST'] variable and customize the output per domain that way.
Benefits with this method:
1) it can be done already, no need to change anything with DA.
2) you can easily have it default to one message if you have not setup any customized text for that domain.
John