Cross Branch Browse for TinyMCE

sazzct

I am trying to do a cross branch browse within TinyMCE. I have the code to do it as a callback for textfields within a DCT and was going to leverage that code within tinyMCE.
According to the TinyMCE website, it says to edit the tinyMCE.init() to just set
file_browser_callback: CustomJSCall;


This does not seem to be available through the TS interface,
I thought I could with the following call:
IWTinyMCECustomConfig("custom1","file_browser_callback","AssetBrowse");

but from the teamsite documentation, configuring callbacks in this way is disabled....
And, it did not work...
So, the question is, how do I set the file_browser_callback?