How can I protect Amazon SimpleDB from SQL Injection?

Under the principle of "if it walks like a duck and it sounds like a duck," it sure seems like the SQL-flavored queries that Amazon's SimpleDB supports should be susceptible to SQL injection-type attacks. Here's a simple example that assumes the attacker's input is going into the variable $category, and that he can guess a column name:

$category = "Clothes' OR Category LIKE '%";
$results = $sdb->select("SELECT * FROM `{$domain}` WHERE Category = '$category'");

If you're playing the home game, these lines can be an in-place replacement for line 119 in the file html-sdb_create_domain_data.php in the sample code in Amazon's PHP SDK (1.2).

Amazon publishes quoting rules, and I suppose I could write something that ensures that any " or ' in user input gets doubled up... but I've always understood that escaping is basically an arms race, which makes parametrization my weapon of choice when using, for example, MySQL.

What are other people using to defend SimpleDB queries?