How to set date_modified through REST API

I want to set the date_modified field of Notes that I am importing through the REST API. However, I can't see any way to turn off the automatic updating of date_modified in the REST API, if I try setting update_date_modified to false this has no effect.

An example of data I am sending via an HTTP PUT:

   "update_date_modified": false,
   "date_modified": "2016-02-09T10:12:52.0000000"

The request works but the date_modified is set to the date of the request, not the value I set