A quick test by removing the JS validation validate-url
seemed to work without any issues for me, so with that in mind:
/app/code/core/Mage/Adminhtml/Block/Catalog/Search/Edit/Form.php:
In function _prepareForm()
Change this:
$fieldset->addField('redirect', 'text', array(
'name' => 'redirect',
'label' => Mage::helper('catalog')->__('Redirect URL'),
'title' => Mage::helper('catalog')->__('Redirect URL'),
'class' => 'validate-url',
'note' => Mage::helper('catalog')->__('ex. http://domain.com'),
));
To this:
$fieldset->addField('redirect', 'text', array(
'name' => 'redirect',
'label' => Mage::helper('catalog')->__('Redirect URL'),
'title' => Mage::helper('catalog')->__('Redirect URL'),
//'class' => 'validate-url',
//'note' => Mage::helper('catalog')->__('ex. http://domain.com'),
));
NOTE: obviously do not just edit core but extend the Adminhtml Block.