As far as I can tell from the source, it seems like the user has no input to control the prefix of the uploaded code. The s3.upload_fileobj() is used but the key that would normally contain the prefix you wanted is hardcoded as shown in the linked line. I suggest that either the user can specify another command line option such as --prefix and give a prefix that way, or to add the functionality to --bucket, where I can write my-bucket-name/prefix and it will parse out the prefix, putting it as the start of the key parameter.

https://github.com/aws-samples/sagemaker-studio-image-build-cli/blob/master/sagemaker_studio_image_build/builder.py#L30