Intarsia by "sliding loop" method

Has anyone mastered the “sliding loop” method for intarsia that was described by Rick Mondragon in Threads and Knitter’s Magazine a few years ago?

I have the article, and for some reason I thought this method would work in the round, but the article doesn’t mention it.

Edited to add: I think I understand the method as the author explains it, but he casts on each new block of colour next to the last one, adding to the left or right. I am in the middle of knitting a sock and want to add an intarsia block of colour, so it’s the cast-on that has me stumped.

This person has a video showing how the loop works to attach a second block of knitting:

She uses it to attach a lace edging, but the idea is the same.

My problem is, I need to attach a block on both sides, and I’m not sure if that is possible with this method.

Can you cast on as usual with the two colors and then work the sliding loop on the next row? The tail from the cast on can be used to close up the small gap between colors at the cast on row.
To add a block on each side of a finished project could you work one block bottom to top and the second top to bottom?

I will give it a try and report back – thank you for the suggestions!