I'm pretty sure you could have found the solution by searching SCN, but anyway:
CALL FUNCTION 'LIST_FROM_MEMORY'
TABLES
LISTOBJECT = LT_ABAPLIST
EXCEPTIONS
NOT_FOUND = 01.
CALL FUNCTION 'LIST_TO_ASCI'
TABLES
LISTASCI = lt_output
LISTOBJECT = LT_ABAPLIST
EXCEPTIONS
EMPTY_LIST = 01.
LT_OUTPUT is now filled with a number of (256-char) lines, showing
what would have otherwise appeared on the report (lines and all).