Divide a fileTree into parts to run in separate ant batches

Thanks so much. Is there a way to define a separate system property per batch? I want to set a runner number. I tried to put sysProperty(key: “runner”, value: i) in the batchtest block, where the value of i increments for each batch. Like below:

  batchtest(todir: "${testDir}") {
     ant.filelist(dir: "${targetDir}", files: batch.join(","))
  }

But I get the following error: batchtest doesn’t support the nested “sysProperty” element
Is there a way to set a system property for each of the batch tests? Assuming they are run on separate JVMs