Creating ad hoc groups

It doesn't seem to be possible to create custom groups for one-off tasks that you may only need for a limited period, i.e. if I have a short-term task/project involving a group of people I have to tag them all individually in Wrike messages, rather than being able to create a temporary group. A permanent group set up wouldn't be appropriate for this - it would be useful if a task owner could create an ad-hoc group for the duration of a particular task.