Thanks golka! I needed this tonight and you saved me some time...
For posterity, here's what the batch looks like:
var updateModStatus = "<Batch OnError='Continue'>" + "<Method ID='1' Cmd='Moderate'>" + "<Field Name='ID'>" + niemApp.projectID + "</Field>" + "<Field Name='_ModerationStatus'>0</Field>" + "</Method>" + "</Batch>";
Cheers,
Matt