The "Central Authentication Service" page can be redirected to another page by using the loginurl parameter on CAS.

When you redirect to CAS, you should not redirect just to https://bb5.fsu.edu/cas/login?service=http://cfprod.ais.fsu.edu/sfs/das/ or similar, but you should add the loginurl parameter and give it Blackboard's login page. The final URL should look like https://bb5.fsu.edu/cas/login?service=http://cfprod.ais.fsu.edu/sfs/das/ &loginurl=https://campus.fsu.edu/webapps/login/bb_bb60/logincas.jsp on production.

The test CAS URL should have either &loginurl=https://dev.campus.fsu.edu/webapps/login/bb_bb60/logincas.jsp or &loginurl=https://staging.campus.fsu.edu/webapps/login/bb_bb60/logincas.jsp appended depending on whether you're using test or staging (or if you don't want to figure out which is which, only use one of them).

This should at least give the student the Blackboard look and feel on login.