I don't think any documents cover that specifically.

To do it, you'd need to use a memory mapper. Set up your screen so the upper part of it uses 256 tiles. That give you 8 rows of tiles, if there were none being repeated. Then set up the lower part/s of the screen using a different 4k background CHR. Using a sprite #0 hit, or timed code if you need to do more than one bankswitch (use 113.666 cycles per scanline - yeah, it's not a whole number, just have 2 114 cycle loops and 1 113 cycle one consecutively for proper timing). When the PPU is rendering the appropriate scanline, write to the memory mapper to swap the banks. It might be kinda tricky, but it's not too difficult to do. Check out some of Chris Covell's demos for examples.