PR restriction for components added via Work order

Dear Gurus,

I know my question might sound a bit stupid, but maybe you will give me the right direction. The concern is: business purchasing csdt materials through network(mostly non-stock), issues by work order(stock ones). When these stock materials qty is 0, instead of purchasing through network, they just add them into Work order, which will generate PR in demand of added qty. Same time, purchasing team starts purchasing the same material through network. So as a result, material purchase gets doubled and its extra expenses. So is there any possibility to restrict generating of PR for materials(csdt) added through WO, but allows through network order?