What does "volume" mean in MAX_IOPS_PER_VOLUME?
A "volume" is either a drive letter, or a raw partition in SQL Server.

For a resource pool configured for X maximum IOps per volume where a query uses tempdb, splitting that tempdb across multiple volumes on a single physical disk, SSD or not, with the data on a single volume may well give you the granularity you desire.  As always, I'd test it.