How to integrate a multisite indexer cluster with remote standalone Splunk installations?

Dear Splunkers, We have a multisite Indexer Cluster in our datacenter and some remote locations with local standalone Splunk installations. Now we want to connect our search heads of the datacenters to those remote Splunk installations. It's important for us to use Splunk Search Group of search peers because we just want to search those remote Splunk installations when needed to save bandwidth. I saw on distsearch documentation that we cannot use cluster and search group functions at the same time. Does anyone know how can I integrate those two Splunk installations? Thanks!