Yii2 ActiveForm CheckboxList Group Seperator

I am trying to place a line in between a list of values in a Yii2 CheckboxList. For now I am just trying to get it to work using the yii Bootstrap 5 Html form field.

When using this:

      <?= Html::checkboxList('field_name','',[
            'organisation_name'=>'Organisation Name',
            'organisation_vat_number'=>'Organisation VAT Number',
            'invoice_number'=>'Invoice Number',
            'invoice_date'=>'InvoiceDate,], 
     $options=['separator' => '<hr>', 'class'=>'form-control']) ?>

I get this:  

Organisation Name   
---------------------------
Organisation VAT Number
---------------------------
Invoice Number
---------------------------
Invoice Date
---------------------------



What I want is this:

Organisation Name   
Organisation VAT Number
---------------------------
Invoice Number
Invoice Date
---------------------------

Is this possible with HTML Bootstrap and how to implement with Yii2 ?

What I am thinking is to create a custom item rendered using the $index.

Edited: Another workaround is to use the $key as a flag for your "separator".

<?= Html::checkboxList('field_name', '', [
    'organisation_name'       => 'Organisation Name',
    'organisation_vat_number' => 'Organisation VAT Number',
    
    'separator'              => '',

    'invoice_number'          => 'Invoice Number',
    'invoice_date'            => 'Invoice Date',
    'another_menu'            => 'Another Menu',
    'another_menu'            => 'Another Menu',
    'another_menu'            => 'Another Menu',
    
    'separator'              => '',
], [
    'item' => function ($index, $label, $name, $checked, $value) {
        if ($value === 'separator') {
            return '<hr>';
        }

        return "<label class='form-control'>" . Html::checkbox($name, $checked, ['value' => $value]) . " $label</label>";
    }
]) ?>

Our homework is to put the 'separator' key anywhere inside the array of $items.

Result: