For Stored Processes viewed in Portal, I would recommend building a prompt window from scratch. You will have more flexibility for styles and layout.
'from scratch' - can be done in a variety of ways:
1. web page HTML form (Portal would point to the .htm/.html page)
2. Stored Process html form code -
http://support.sas.com/kb/37/050.html (portal would point to the stored process)
3. Custom Input Form -
http://support.sas.com/kb/38/621.html (portal would continue to point to your current stored process view where this custom input form would be presented.)
~ Angela