This is what worked for me. If you have the oid, then all you need to do is:
<?php
$pdo = new PDO($dsn, $user, $pass);
$pdo->beginTransaction();
$data = $pdo->pgsqlLOBOpen($oid, 'r');
header("Content-Type: $mime");
fpassthru($data); ?>
The beginTransaction() is required, if you want to $pdo->commit() (it's not required) then do it after the fpassthru.
On a side note, those using Zend Framework can call getConnection() on the standard PDO database object which will get them the $pdo object as above. Then just remember to disableLayout() and setNoRender() as necessary.
