Nope, currently it's not possible to do it and as far as I know, and you can see in the issue below, Atlassian do not plan to deliver this feature any time in the future.
See https://jira.atlassian.com/browse/JRA-1330 for discussions, reason why you can't do it, and LOADS of workarounds.
Including a plugin at https://marketplace.atlassian.com/plugins/com.quisapps.jira.jfs
I hope it helps!
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