This is possible. Please go through this sample video which explains how to achieve it.
Let us know if you need any more information.
Presenter loads the characters from Presenter Assets Character set.
Inside Presenter Assets->Characters, there is a file named characters_localisation.xml.
You will need to edit it and make an entry inside it like this:
You may add other language names if you are using any other locale. Sample is present in the characters_localisation.xml.
Make sure that the folder you create is also named xtras.
After following the above steps, you will see the category xtras in the drop down menu.
Hope this helps.
I have created a document that shows step by step instructions from the editing of the XML file to the creation of the Image and Thumbnail directories to getting the Face to show in the character chooser. I don't see an option to attach a PDF to the forum but if anyone is interested, the can email me at email@example.com and I will be happy to share.