Hello,
There's no method or class to use the preprocess method standalone, but we can create a small class to acomplish it. This is a class to clean templates and save them, so they can be reused setting preProcessed as true. After you have purchased a license, please write to contact[at]phpdocx.com and we'll send you this class.
About raw option, please check its description on
http://www.phpdocx.com/api-documentation/templates/replace-variable-text-Word-document
The best and faster approach in your case would be use the custom class to generate preprocessed DOCX and then use replaceVariableByText setting raw as true.
Regards.