Yes, I understand the logistical challenges of working around ML's 1s minimum limit for bucket_span, and I created an enhancement request for the development team that references this forum entry, but honestly, without a complete understanding of the use case (i.e. something that we fully understand and can assess if it is truly applicable to many of our users and not merely an inconvenience for you) then I'm not sure how aggressively this will be prioritized.
For the time being - it would seem that your workaround is good enough to get you by with your offline analysis. The product, used in the way that you describe, should be able to detect anomalies in your time-scaled data.