I came across to handle this by inheriting default_get method of the sale order that contains the one2many order_lines field in which I return the values to this field

def default_get(self, cr, uid, fields_list, context=None):
   res = super(sale_order, self).default_get(cr, uid, fields_list, context)
   res['order_lines'] = (0, 0, { 'here_the_field_name_of_order_lines_comodel': 'values_goes_here' })
   return res