It seems this PenPy think does not allow to start external programs, such as other games.RenPy is a open source visual novel engine used mostly to create such jap dating stories.
We can use it to create a game story and a clickable game world map. Than wen the story permits, use it lo launch SPRING with a particular mission as a lobby does.
Go here to learn about game making/scripting for spring:
http://springrts.com/wiki/Lua_Scripting
http://springrts.com/wiki/Game_and_Unit_development