u can inherit that view like :

<record model="ir.ui.view" id="view_sale_order_graph_inherit">
    <field name="name">sale.order.graph.inherit</field>
     <field name="model">sale.order</field>
     <field name="inherit_id" ref="sale.view_sale_order_graph"
     <field name="arch" type="xml">
         <xpath expr="/graph" position="inside">
             <yourelement>
             </yourelement>
         </xpath>
     </field>

     

 
dont forget to depend ur module to sale and xml view in __openerp__.py