Middle playeres are defined as those who are no longer new to the sport, but also haven't reached the elite level yet, or simply just don't care to play at the top level
At a board meeting, define the small and large tasks that middle players can help with.
To further specify the tasks and how to do them
Notice who works with which tasks
The workshop should be for all players
Poke and complement players personally about the tasks they would be good at.
Approach the players about the tasks they worked with at the workshop
Repeat the three steps at least once a year.
Doing it every season (e.g. indoor/outdoor) could also be a good idea.
Encourage attending local pickup games
(Friday Hat , KFK Summer League, etc...)
Look to what is done in other cities/countries
(Malmö, Belgium, etc...)
Local and international tournaments "only" for middle players