Changing Material Expense Accounts in EAM

I have a requirement where I need to change the material expense accounts on a work order based on what I am buying. For example services would have a different accounting distribution than purchased parts. I can change the WIP accounting class on the work order to partially accomplish this, but if I have both on a work order, changing the wip accounting class at the header only gives me the correct accounting for one on the items. Does anyone have any suggestions on how I can make this work. I am new to EAM so any help I can