For anyone else in the same boat- it turns out the default knowledge builders already account for this (hence how the Evaluation demo is able to work). The png file needs to be {process.id}.png instead of {process.id}-image.png.
So, to depoy a bpmn process without using Guvnor from Eclipse:
-Put the bpmn file into the "jbpm.console.directory", which by default with the demo is ${install.home}/sample/evaluation/src/main/resources
-Create a PNG using the 'export png' option from the eclipse plugin, and name it {process.id}.png - i.e. com.sample.bpmn.hello.png
-Create FTL files by hand or by using the "generate jBPM forms" option within eclipse
-Put the PNG and FTL files inside the classes folder of the gwt console server (i.e. jboss-as-7.1.1.Final\standalone\deployments\jbpm-gwt-console-server.war\WEB-INF\classes\ ) - although anywhere on the gwt-console-server classpath should work
-Restart jboss and you are good to go.
For how extremely simple this process is, it sure took a long time to muddle through and figure out how to do it.