purchase_view.xml

<?xml version="1.0" encoding="UTF-8"?>
<openerp>

	<data>

		<record id="account_fiscal_position_rule_purchase_order_form" model="ir.ui.view">
			<field name="name">account.fiscal.position.rule.purchase.order.form</field>
			<field name="model">purchase.order</field>
			<field name="inherit_id" ref="purchase.purchase_order_form"/>
			<field name="arch" type="xml">
				<field name="partner_id" position="attributes" >
					<attribute name="context_fiscalrules">{'company_id': company_id}</attribute>
				</field>
				<field name="dest_address_id" position="attributes" >
					<attribute name="context_fiscalrules">{'company_id': company_id, 'partner_id': partner_id}</attribute>
				</field>
			</field>
		</record>

	</data>

</openerp>