Hi Oliver,
We can not priorities any registered queues but yes we can de- regestered other queue when traffic increases.
there is another way you can achieve you requirement. You need to use SAP standard report RSQINWKEX and need to schedule it as a back ground job.You need to create a variant where you save the Groupware queue name example .CSA* to that it only run for a specific queue. when it will run it will pick all the groupware queue and change there status to running stage . I have schedule it in my project.and it\s working fine. job duration will be 5 minutes as it's very small report.
you can test it before implementing it up to you.. 
Thanks,
Prem