Rang the lovely Bill King and he's explained the supersize cable method - I had written it down when it made perfect sense, but then afterwards, of course, it was complete gibberish!
The supersize cable method is a way of creating really wide cables, without having to use a length of seperate yarn. Basically you split the crossover into two or more sections, and cross it gradually. This is how wide cables are created in industry. You need a ribber, and a multi-transfer tool.
For example, say you wanted to work a 5 x 5 cable. Set the needles up as follows:
ooooooooooooooooooooo <- this row is at half pitch
Ribber is set to half pitch, and the two needles in work are opposite the out of work ones on the main bed, to create the "channel" down the sides of the cable.
K 4 rows to set the pattern.
Put two needles up on the ribber bed, roughly between needles 5 & 6 on the main bed. K one row, then drop the new sts. This adds slack for the crossover.
Pick up sts 6-8 on one tool, and sts 1-5 on another tool. Pass 6-8 to the back and put on needles 1-3. Replace sts 1-5 onto 4-8. K a row.
So you have:
K another row, adding two more sts on the ribber, K a row and then dropping the new sts.
Pick up sts 9-10 and 1-5 on seperate tools. Pass 9-10 to the back, and place next to 6-8. Replace sts 1-5 on the right hand end
You should now have:
K rows to next cable and repeat.
Of course, you could do far larger cables with this method. You shouldn't try to cross more than about 3 sts max at a time, though, so the wider the cable, the more crossover rows you'll have to do.