R help - Jan 2013 - Appending BSON arrays in MongoDB with package 'rmongodb'

Dear list,

I simply can't figure out how to append an BSON array in MongoDB (with 
package 'rmongodb') using either the '$push' or
'$addToSet' operator.

It's sort of the last missing puzzle piece regarding CRUD operations, so 
any hint will be greatly appreciated! Below you'll find a link to an SO 
post where I provided a reproducible example and additional information 
regarding MongoDB: 
http://stackoverflow.com/questions/14489612/problems-with-mongodbs-push-operator-rmongodb

Thanks a lot and best regards,
Janko