How to join independent text threads?

InDesign CS6:

I have a document set up as follows:

Pages 1, 2, 3 - each page has a single text block threaded to the next page.

Pages 4, 5, 6 are similar - each with a single text block threaded to the next page.

This sort of set up repeats for a total of around 100 pages.

All the pages / text blocks area already filled with text.

I'd like all text blocks to be threaded together - eg a continuous text thread through the document.

How do I join these independent, already filled, text threads together?

I've searched the manual and more - but can't see the answer I'm looking for

Thanks!