codeigniter form_validation is_unique compare data between tables

I have a from which lists several items that can be selected by check box and a dropdown permitter added. In a separate part of the form is have another check box. This is submitted as two arrays.

The arrays look like this

Array
(
[1] => Array
    (
        [num_copy] => 1
        [dwg_rev] => B
        [dwg_id] => 1
    )

[2] => Array
    (
        [num_copy] => 1
        [dwg_rev] => B
        [dwg_id] => 2
    )

)
Array
(
[1] => Array
    (
        [client_id] => 1
    )

)

I need to pass these two arrays to a form_validation that can check is dwg_rev has already been added to the database for the selected client_id.

I tried to use is_unique, but it can only check in one table to see if this already exists in it.

This is what my form validation currently looks like

$rows = array();

    if(!empty($_POST['result']))
    {
        $rows = $_POST['result'];
        $temp_dwg_array = array_column($rows, 'temp_dwg_id');
        foreach($temp_dwg_array as $key => $temp_dwg_id)
        {
            $this->form_validation->set_rules('result['.$temp_dwg_id.'][dwg_rev]', 'Revision' , 'required|callback_check_issued_rev');
        }
    } else $this->form_validation->set_rules('result[][temp_dwg_rev]', 'Revision' , 'required');

    if(!empty($_POST['client']))
    {
        $temp_client_array = array_column($_POST['client'],'client_id');
        foreach($temp_client_array as $key => $client_id)
        {
            $this->form_validation->set_rules('client['.$client_id.'][client_id]', 'Please make a selection from the distribution list' , 'required|callback_check_issued_rev');
        }
    }
    else $this->form_validation->set_rules('client[][client_id]', 'Distribution' , 'required');

I want to create a callback function, but I can't figure out how to pass two variables to the callback function to compare to the db.