well then you got a starting point ...
Run a SQL trace (not for hours just for those specific problimatic queries) and get the Dev's to execute all or some the bad running queries (they identified) ...
The SQL trace will record these and you can select the execution plan in the SQL trace for these queries as well. Can help you find out what and how sql is processing the queries and help you decide where the minimal change can make a beg difference ...
MCITP: Database Administrator 2005
MCTS SQL Server 2008
MCP SQL 2012/2014
MCSA SQL Server 2012/2014
MCSE Data Management and Analytics