OK,
You can create your own ROLL/CRAWL type group, but the first take item in ROLL group should recall a specific take item number (in order to show the background) and the last one other take item number (to take background offline) using a script.
dim takeitem as xpBaseTakeItem
engine.sequencer.GetTakeItemByID(101, takeitem)
takeitem.Execute
In my example the first roll item recall take item no 101 (Background ON) and the last/second one recall 102 (clear the background Layer and take it offline).
The script is launched when the event is "visible".
Link: https://www.dropbox.com/s/w44lc26zd3hln84/Credit%20Roll%20%2B.xpf?dl=0
Have FUN!
Gabriel
#XPression