Workaround
1) Update a LOV to have a second field as lookup to send a key for the string value. An index rowcount can accomplish this by adding it to the LOV query
2) use the universe to use a do a decode object take a valid value and translate it into what ever string the report needs
e.g. take "Period _1" and return to report the date range string "April 1, 2013-March 31, 2014"
LaunchWorks
Looking to send strings such as "April 1, 2013-March 31, 2014" in Activity Launch to schedule report external
This is a multi select LOV for multiple date ranges (string format)
example: April 1, 2005-March 31, 2006; April 1, 2011-March 31, 2012; April 1, 2012-March 31, 2013; April 1, 2008-March 31, 2009