Torque has its limitations, Truce isn't some sort of god that is capable of breaking these limitations.
Even if you did use decals for this, how are you going to send them to other players? Have each player manually send the file to the host, the host puts it in a certain folder, and then everyone rejoins?
The only potential way I can see around this is if TCPobjects can handle sending images, and even then there's so many reasons why that would be a bad idea.
In order for this to work it needs engine modifications to support uploading and downloading of images while the server is up and clients are in game.
Why would you even want this though? We've all seen what people have done with the server preview images, imagine what people could do with this.