Stop an input field in a form from being submitted

You could insert input fields without "name" attribute:

<input type="text" id="in-between" />

Or you could simply remove them once the form is submitted (in jQuery):

$("form").submit(function() {
   $(this).children('#in-between').remove();
});

The easiest thing to do would be to insert the elements with the disabled attribute.

<input type="hidden" name="not_gonna_submit" disabled="disabled" value="invisible" />

This way you can still access them as children of the form.

Disabled fields have the downside that the user can't interact with them at all- so if you have a disabled text field, the user can't select the text. If you have a disabled checkbox, the user can't change its state.

You could also write some javascript to fire on form submission to remove the fields you don't want to submit.