it seems that this won't work either since so many of the ParserOptions are retrieved from global settings in strange ways.
Strange? They are loaded from either initialiseFromUser() or one of its setters...
If you can do a regEx that will work for such substitution that would be great, or the server could do some transform that represented the transforms in JSON so that the template parsing could be avoided ..
I remember some time ago we discussed in wikitech-l the possibility of doing a late replace of plural: and {{sitename}} to have the rest of the message parsed in a cache.
It may be worth to bring back that idea if such light parser is going to be done in JS too.
For transforming the templates into a JSON tree, the DOM preprocessor may be easy to transform.