AWS Transfer S3 User Directory Creation Case Specific

I am using the AWS Transfer service with S3 buckets for storage and a chrooted dynamic path to create the user directory as the user is authenticated - "/mybucket/${Transfer:UserName}".

This is working as expected except that when the ${Transfer:UserName} variable is used to create the user directory it matches the case that the user name was entered on the client. Authentication is via the AWS Directory service. As this is a windows system there is no distinction between lowercase and uppercase usernames.

E.g. if the client specifies the username in lowercase the user directory is created in lowercase. If the client specifies the username in uppercase then the user directory is created in uppercase. This can result in multiple user directories.

Is there a way to force the case of the user directory to lowercase when it is created using the ${Transfer:UserName} variable?