MongoDB $addToSet Functionality

Hi there, may I know is DreamFactory currently supporting $addToSet function in MongoDB?

For example, currently i am having data as below
{
"_id" : ObjectId(“12345gthtrh”),
“letters” : [ “a”,“b”,“c”]
}

Currently, my use case is $addToSet to property letters.
In MongoDB command, it should be like this
db.letters.update({"_id": ObjectId(“12345gthtrh”)}, {$addToSet: { letters: “d”}})

The result will be
{
"_id" : ObjectId(“12345gthtrh”),
“letters” : [ “a”,“b”,“c”,“d”]
}

Which DreamFactory API call should i use to support $addToSet function in MongoDB? Since PUT will replace the entire set of data, and PATCH will update the changes of the data, which will not be appending into the current array of dataset.