I haven't tried so not sure. This may be related to http://forum.jasonette.com/t/html-as-background-not-rendering/773 so if you try the solution I gave on that thread and it still doesn't work, it means it doesn't work. If it does, then well it does. If you do try out, please keep us posted on what happens.
The preload.json has an intentionally stripped down implementation compared to the previous approach of
loading.json, because the assumption was that people won't use preload screen to do all kinds of complex things but just want a simple loading screen until the main screen loads. (And trying to support everything was introducing all kinds of buggy behaviors so wasn't worth the trouble)