there is a simple but cool solution. The customer has (even if the
support has ran out already) at every time the right to upgrade to the
last version which was accessible at the last day of his running
support. He can have a look at the JIRA versions and look, which version
was available that day and just take this one to install. If support
ran out one month ago, he is capable to upgrade to JIRA 7, what should
clear his problems.