I suggest you set
up multiple WBS, so materials have a code, say XX1, labour can have a code XX2, then it doesnt matter what work package they are under, its just another method of sorting and reporting. In this way you can report overall progress of the work package, and separately report % complete for materials overall, materials within the work package etc etc. This is the way I have set up controls for years.....client WBS, internal multiple WBS, discipline WBS Area WBS.