Allow support request from within JIRA to become a comment on an existing support case

Sometimes customers have already created a support case in https;//support.atlassian.com, and then we ask them to append their logs and/or an XML backup. Some customers find this a little challenging, in which case we ask them to create a support request from within their JIRA instance.

It would be great in the circumstance of when there is already a support case, that the user be able to specify the key of an existing issue in https://support.atlassian.com, and instead of creating a new case, https://support.atlassian.com appended the attachments to the existing issue, and added the subject, description and all other fields into a comment on the existing issue.

I tested if this works already, by using the key of an existing issue in the subject. It doesn't work. A new issue is created.