Remove name attribute - Form API
Assuming it's a textfield, I think the simplest way would be via a preprocess on theme_textfield:

function MYMODULE_preprocess_textfield(&amp;$vars) {
  // Identify the element and remove the name property (which will always be present)
  if ($vars['element']['#foo'] == 'bar') {
    unset($vars['element']['#name'];
  }
}


Bear in mind that Drupal won't be able to process the value for that field correctly if you submit the form, but I guess you're submitting this offsite anyway.

If it's not a textfield you should be able to use the same principle with the the theme function for whatever element type you're using.