Resurrecting for a bit - I'm in a similar situation, but I actually use two gcodes per filament - Linear Advance (M900) and Steps/mm (M92). Both of these can vary per filament - material type, viscosity, that kind of thing. I suppose I can reverse engineer the above plugin and add an additional setting for Steps/mm - any chance there's been discussion of adding a generic 'Start Gcode' field to the Material Preference tab? I'm accustomed to doing this in Slic3r and Simplify and prefer supported solutions when possible.