Well, I decided to dive into the Template Toolkit code, and I have developed an extension which allows one to selectively auto-filter all insertions of variables and simple expressions in a block.

Unfortunately, I can't get subscribed to the Template Toolkit mailing list (http://template-toolkit.org/mail/index.html). I get a 404 error when I try to confirm my subscription via HTTP. If anyone is on the list and can get the attention of the list manager I would appreciate it. I would like to share and discuss this change with the rest of the group. Thanks!