This a quite old post but I think this is still impossible to achieve that 
, even with 1.5 SDK.
The main problem is not sending a custom file through a property (you can use the default css property, I've already use it to push .json file, even .bat file), but is how you can access this file through SDK, because there is no way I know to get the complete URL path to the file.
Br,
Vincent