Since every named replica may have a different service level objective and thus be used for different use cases, there is no built-in way to direct read-only traffic sent to the primary to a set of named replicas. For example, you may have eight named replicas, and you may want to direct OLTP workload only to named replicas 1 to 4, while all the Power BI analytical workloads will use named replicas 5 and 6 and the data science workload will use replicas 7 and 8. Depending on which tool or programming language you use, strategies to distribute such workload may vary. One example of creating a workload routing solution to allow a REST backend to scale out is here: OLTP scale-out sample.