Mr. Metzger, please try one of these. Honestly I'm not sure if these are the rubato styles or not. My Korg is put away right now and I can't easily move things around to set it up. I would upload the original one that I made on my PA-50 but that's on Floppy and I don't have access to a machine that even reads floppies right now.
I'm a little rusty on the Korg operating system. I believe you will have to embed them in a "set" folder in order to upload them to the board. Please let us know if any or all of these work.
If they don't work, please read my posts on the Korg PA80 forum. If you understand the theory, it's really not that difficult to make one of these styles yourself, and it will impart to your MicroArranger the "Bass and Lower Backing" function that's found on upmarket Korg arrangers beginning with the PA1X. Yamaha's "freestyles" such as Ethereal Movie work on a similar principle. IMO, this functionality (or some styles like this) should be factory issue on all brands.