Smooth scrolling could be achieved in character mode by making the borders wider, hiding 2 columns or 1 row, depending on the direction. The visible area could then be adjusted on a pixel-by-pixel basis, revealing the hidden content gradually.
Multi-way scrolling was common for BBC Micro games, as the hardware directly supported the barrel-type scrolling described in the article, though only on a full-screen basis. Uridium programmed the CRTC in a particular way, however, allowing the screen's base address to be set halfway down the screen, giving a stationary area at the top and a fixed area at the bottom.
I think the only other game of the period that did anything like this was Firetrack (https://www.youtube.com/watch?v=8bxdd2_qrpg), which used it to get smooth vertical scrolling.
The technique is easy to do (http://www.cpcwiki.eu/forum/programming/rupture/), but you do have to know the trick! It's know a well-known thing, and there's a couple of modern BBC Micro games that use it.