Just off hand by doing a quick look at the available (slim) Mobile Atlas Creator documentation, I'd say you can't directly. You might be able to use the Tile Store settings to download the map tiles locally and then load them into an mbtiles db, but: 1) there are easier ways to do that and 2) you'd be violating most of the terms of use from online tile sources (imho). From what I can gather in a 15 minutes scan, it looks like MAC is designed to create data formats that can be used directly by several types of GPS, most likely in proprietary formats, not something that route-me directly supports. Of course you could write your own tile source interface to access those formats, but it'd probably be much easier to use your own tile server or something like tilemill to setup your tiles for offline use.
-- Randy