Want to use variable in s3_bucket

It seems to be impossible to use variables in s3_bucket.

My use case is to store events in different s3 buckets based on the event tag.

When I'm trying to specify bucket name like this:
s3_bucket s3-${tag}

I've also tried to use parts of the tag like ${tag[1]} without success. Is there any option to make it possible with any workaround?