Hi @lsteele,
As of OJS 3.4 (and subsequently in 3.5), this functionality changes: when going to add/edit any email templates there is the option to “Insert Content” in the email template, from there you can choose from a list of variables that ought to work within the specific template. To get a feel for this, you can try it in the Workflow settings in our 3.4 test drive: https://pkp.sfu.ca/software/ojs/demo/
-Roger
PKP Team