[Coding] Thumbnails in FileBrowser

[Nickon7777]

Hi All!
In my plugin I want to make a possibility to see thumbnails when the user opens the file browse dialog (like VaM person appearance dialog can: it shows a .jpg file with the same name as a preview).
For that I use code like following:

string ext = "custom"; // "json", "vap",... work fine
SuperController.singleton.GetMediaPathDialog(callback, ext, PLUGIN_DATA_DIRECTORY, false, true, false, null, true, null, false, false);

Unfortunately it works only for VaM-reserved file extensions like "vap", "vam", "scene", etc. If I understand correctly from FileBrowser.CreateFileButton() implementation those extensions are hardcoded and there is no way to make it work for some custom file extension. Hope I am wrong and someone help me to find the solution.