I figured this out a couple weeks ago and it makes some new things possible. The main things it can be used for are:
1) Stacking several 2(or more)x1 divider items in the corner of a room then merging more divider items into them.
2) Stacking large items in the corner of a room where they usually occupy tiles which rollers can't access (think anything 2x2 or larger) as well stacking items which were before completely off limits (for example you could stack 2 or more T-Rex statues or Epic Fireplaces now if you wanted to).
I'll run through an example of the first stack mentioned above and then intuition should let you understand how the method works and you'll know how to do the second one. I'll also assume for convenience sake that everyone knows how to stack sofas and dividers because the guide utilizes both (also it seems likely that it will only be useful for people who know their stuff anyway).
1) First stack all the items you want on one side of your stack in the corner as you normally would. Here, I've used bookcases. Of course it works for any divider. At this point I should mention it does not work for sofas or any variant thereof due to how it works.
http://oi43.tinypic.com/2s7do5k.jpg
2) Once you've got all the dividers you want on one side, roll a chair onto the square you want to add things to later. Since I'll be merging more bookcases into the corner square, I've rolled a pod onto the corner square. Once your chair is rolled in, remove any ditches that are underneath the pod. At this point it is also worth your while resetting the height of the other side of the stack if you want to add a rug / carpet underneath (which I will be doing of course because I'm a classy mother******).
http://oi41.tinypic.com/i2onwl.jpg
3) Now the new stuff comes into play. First, take note of how many more dividers you are going to be adding in. In my case, I'll be adding 2 more bookcases: one at ground level, and one on top of that. Now I need to roll a tile onto the pod. Do so as you normally would for sofa stacking. Technically speaking this tile just needs to be higher than the pod for it to work, but I prefer to do it high up so I can see it and it's easier to remove later. Once the tile is in, now roll in a table item at the height you want the highest item of your stack to be at. So here, I've rolled a ditch in at the height I want my highest bookcase to merge in at.
http://oi43.tinypic.com/2zhmvpw.jpg
4) Now roll a second tile onto the pod, but this time at a lower height than the first one. Then roll a second table item in, this time at the height you want your next lowest item at (for me it's my ground height bookcase so I'll be rolling in a ground-level ditch). You can't see my ditch here because it's behind the pod, but it's there.
http://oi44.tinypic.com/qq69mq.jpg
5) Now, for reasons I can't be bothered explaining (they'll become intuitive as you play around with the method but in this case it's because I want to use a big rug) you have to repeat some steps again, this time on the other square that's beside the pod. Put another chair down next to the corner square, and roll another tile high up onto it. Then roll another table item onto this new chair, again at the height you want your highest item to go on at.
http://oi44.tinypic.com/20pdiqo.jpg
6) Now do the same as you did before: add another tile but lower than the first one, then add a second table item, this time where you want your next item to be.
http://oi43.tinypic.com/2d0yip5.jpg
7) That's all the hard parts out of the way. At this point, you can add your rug. If you hadn't done steps 5&6 then you wouldn't have been able to put any size rug on. You would have only been able to use a 2x2 rug. Once you've added your rug/carpet/patch, put your bottom item on top of the rug. It will go in as if all the other furni wasn't there.
http://oi39.tinypic.com/vo38t3.jpg
8) Once that's done, you now need to carefully remove the LOWEST tiles from the squares which have chairs on them. For me, that's my orange color tile and my marble tile that is partially obscured by the skull candle. Once you remove these lower tiles, you will be able to place your second divider right on top of the first without any resistance.
http://oi43.tinypic.com/10gn3no.jpg
9) At this point, you're stack is done and you can remove all of the tiles, ditches (or other table items) and chairs.
http://oi43.tinypic.com/264jh2q.jpg
And there you go.
