You cannot, I tried, then checked with HipChat support, who confirmed it isn't an available functionality. So I opened this suggestion ticket:
Please vote for it so it will get more attention from the development team. You may also comment to emphasize your use case.
...from the beginning. We have built up a lot of content in HipChat, with it being a core tool in our distributed company model. While it is true that we didn’t need to move to Slack immediately, we felt it...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
You're one step closer to meeting fellow Atlassian users at your local meet up. Learn more about AUGs