I was just thinking about this myself when I came across your post. I looked through the list you mentioned and the author's reasoning behind the order and it seems reasonable. There are definitely too many tie-ins to avoid having a decent break in between books it seems. Keeping in mind that I read TDT 10+ years ago and haven't read any of the tie-ins, here is my suggestion if you absolutely can't do the 7-book, 2-short story break between W+G and Wind Through the Keyhole that Mahfah recommended.
I took his list and just split it up a little bit, making sure that any tie-ins were still before the core books I assume they're related to just in case they introduce a character or concept that doesn't come until after it in the list.
-The Stand -The Eyes of the Dragon -The Talisman
The Gunslinger
-Salem's Lot -The Mist -It
The Drawing of the Three
-Insomnia -Rose Madder -Desperation
The Waste Lands
-The Regulators -Everything's Eventual -Bag of Bones
Wizard and Glass The Little Sisters of Eluria
-Hearts In Atlantis -Black House -From A Buick 8
The Wind Through the Keyhole Wolves of the Calla Song of Susannah The Dark Tower
As you can see, I also kept the last 4 books together since he seemed pretty insistent that they be read back-to-back and I know that a lot of the material from the tie-ins comes cascading in the last three books. Without having very detailed knowledge of exactly what information comes from which tie-in, it would be difficult to try and weave them in there. Plus this gives it a nice 3/1/3 structure for the most part. Given the number of tie-ins, that would be the only way to reduce the number of tie-ins between each DT book. If this structure still isn't enough, someone with much more detailed knowledge of the core books and how the tie-ins actually fit into the story will have to chime in.