All the Player Skins in Sothink Video Encoder for Adobe Flash were created by using Sothink SWF Quicker program. If you are familiar with Flash and the actionscript, you can try to use Sothink SWF Quicker to create skin by yourself.
For the detail steps: please open the sqf file in :\Program Files\SourceTec\Sothink Flash Video Encoder\Controls directory, you can add the content and save the file by yourself.
If we can be further help, please feel free to contact us.
Hope that help and have a nice day.