Trigger Eclipse's code formatter programmatically from a new file wizard

Question

I'm writing an Eclipse plugin with a wizard (org.eclipse.jface.wizard.Wizard) which creates a new file with a basic code template. To simplify the "piecing together" of the file contents, I plan to stuff everything into one long string, inject it into the file, and then call my custom Formatter (inherits org.eclipse.xtext.formatting.impl.AbstractDeclarativeFormatter) to clean up all the indentation and so on.

Question is, how do I go about calling the formatter programmatically? In the wizard I call IDE.openEditor() and get back a handle to an IEditorPart. What can I do from here?