STO with ref to Sales Order

Dear All,

Can we raised STO w.r.t Sales order. My scenario is as follows.

My client has5 0 depots and 3 plant. All sales is always happen from depot. so they use to do stock transfer from factory to depot then sale the material.

In some case customer asked for special material so they raise STo to plant and do stock transfer and then do sales to customer.

Here problem is for special material they have some special price,so they want track in sales order against which STO that material has come because excise will be applicable on special rate agreed to customer.

It is not MTO because sales order is raise at depot.In STO we can not maintain price.

How to mapp this.

Regards

SD Consultant.