j5 stores the schema version of the index each record is indexed in. By configuring the production and standby server to have different schema versions, a reindex will be triggered on failover.
The schema version is stored in C:\ProgramData\j5\data\solr\j5.ini as key schema-version. Set the version in this file on the standby server to some value different to the version on the production server (the default version is 1). Verify that the File System Replication step does not overwrite this file.