CodePipeline S3 source from another account?

Question

What is the way to configure CodePipeline to use as source an S3 bucket in another account? The source block in a codepipeline resource is something like:

  stage {
    name = "Source"

    action {
      name             = "ImportJar"
      owner            = "AWS"
      category         = "Source"
      provider         = "S3"
      version          = "1"

      configuration {
        S3Bucket = var.source_bucket
        S3ObjectKey = var.source_bucket_key
      }
    }
  }

However, the S3Bucket configuration field contains just the name of the S3 bucket and not the ARN. I have cross-account access set up for the bucket and the CodePipeline role has access to it.