Additional features, settings, or issues not covered by specific Microsoft Teams categories
Yeh know that is no the option you are looking for but is the only workaround to do that at this moment.
However keep in mind break out rooms is a coming feature that it will probably be improved, so, If you think this feature is important and want Microsoft to include it, please provide your suggestions or feedback via the link: https://microsoftteams.uservoice.com to improve their products feature. Many features of current programs have been designed and upgraded based on customers’ feedback.
Regarding this point, we would truly appreciate your kind understanding.