Apparently Super Slicer will let you do this as its common when using bases… one support filament on the base and a different on on the model. this saves a lot of filament swapping as the model support can use the same material as the model since it has z spacing, but the base filament sticks to the base as it has none… 
there is no “material modifier” for support
https://www.reddit.com/r/BambuLab/comments/16zuxvl/is_there_a_way_to_start_support_filament_at/