I know this is pretty old but.....good answer always works.
If you're creating a workunit/calling processflow from a cobol program you invoke
1000-open-workflow-db
1000-process-flow
One of the ws fields you have access to is WFAPI-I-WORK-TITLE.
Whatever value you MOVE "WU-TITLE" TO WFAPI-I-WORK-TITLE
appears in the processflow admin tool as the name of the work unit.