Some JSPWiki implementation notes and jots...

The easiest way would probably be to grab the DOM tree after MarkupParser.parse(), and do a series of simple translations. For example, through a custom WikiRenderer.  Storing of the [Mementos] would need to be done in the HttpSession.

!Memento Markup

For simple stuff like CSS, I think it's okay to use
{{{
creole text here
<<%%(font-size:huge)%%>>some huge creole text<<%%>>
}}}

However, for large and complex we probably have to go to mnemonics, such as

{{{
creole text here
<<table(1)>>
}}}

to mark a table.  The cool think about the Mementos is that we can choose either or, depending on the situation.

!Transclusion support

This needs a bit of thinking...  Might be easiest to include the TranscludePlugin.