For subtasks, this can be configured in Administration / Advanced Settings, by changing the columns in the jira.table.cols.subtasks property.
However, Epics are from the JIRA Agile plugin, before JIRA 7 at least, so you won't find a similar option there for Epics. I had a look at the documentation and at the modules of the Agile plugin, and it doesn't look like that option exists.
If you're using JIRA 7, I suggest you take a look anyway in the advanced config and in the system plugin modules. But I'm not hopeful.
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