in this you all ready told that you created on but, you can continue with that,if you refer the module "sale_add_products_wizard" apps, you can easily add that into your function.

i will give you my code , if you can modify it .

def button_submission_submit(self,cr,uid,ids,context=None):
        order_line_obj = self.pool.get('sale.order.line')
        product_obj = self.pool.get('product.product')
        data=self.browse(cr,uid,ids[0]) 
        partner = data.partner_id.id  
        pricelist = data.pricelist_id.id  
        line_ids = data.sale_id.order_line
        for line in line_ids: 
            product_id = line.product_id.id
            p = product_obj.browse(cr,uid,product_id)
            uom_q = p.uom_id.id
            qty_p = line.product_uom_qty 
            product = self.pool.get('sale.order.line').product_id_change(cr, uid, ids,
            pricelist,
            product_id,
            qty=qty_p,
            uom=uom_q,
            partner_id=partner
            )
            val = {
                'name': product['value'].get('name'),
                'product_uom_qty': qty_p,
                'order_id': ids[0],
                'product_id': p.id or False,
                'product_uom':uom_q,
                'price_unit': product['value'].get('price_unit'), 
            } 
            order_line_obj.create(cr,uid,val)
        return True