I don't think it is possible, those dynamic queues are created by RouterOS automatically. You would need to request MikroTik to add an option to change that behavior. In Mikrotik documentation I did not find any configuration option nor did I find a Radius dictionary attribute to affect the name.
One solution would be to not use those automatic queues and create a script to create those queues with your chosen names. The script would be difficult to create. Try writing a perl or php script that pulls a list of your current users from the MySql database your FreeRadius server uses. Have that script create a page on a web server for your RouterOS router to download using the fetch command and create and/or update the queues every 5-10 minutes.
Another solution would be to create manual rules, you might need to have your radius server assign out static IP addresses to keep each client in the proper queue.
I actually don't see the need to change the naming of the queues. Only you and your support staff normally see the queues, you can hide the queues graphs on your web-interface of your router to keep your clients from seeing the queues & queue names.