mikowals:batch-insert ( I am the author ) adds a .batchInsert() method to Mongo.Collection instances. It should work just like basic .insert() with the exception that it handles arrays of documents by using the node mongo driver directly. It has stub method for the client and checks client inserted documents against allow / deny rules.
Issue #1255 tracks adding this feature to .insert(). It nearly made it into the 1.0.4 release with other Mongo changes but now appears to have lost momentum.
I don’t think any command line method of multiple inserts would see much performance gain vs the node driver. The main performance issue is from observing the collection during the insert and that will exist no matter how the changes get into Mongo.