No, it's not supported, but it's what the project file parameter is for.
What is the project file parameter ? i didn't find it documented or didn't notice it when looking through preview.js.
Some type of support for affecting the pre-loader for pre-processing work would be nice. At the moment the support for loading only audio and image leads to problems where plugins that have to do different types of loading are left to load after the game has "loaded". It'd be nice to make loading work for all plugins the way it only does or some.