Passing multiple values with hidden input fields

Use [ ] in the field name to send multiple values:

<input type="hidden" name="your_field_name[]" value="1" />
<input type="hidden" name="your_field_name[]" value="2" />
<input type="hidden" name="your_field_name[]" value="3" />

You will get an array of values in the your_field_name field.