For that type of isometric you can still use "for each ordered" depending on what features you want to have. Using for each gives absolute sorting whereas comparing one object to another is relative sorting, which can prove to be more complicated.
Here is an example with the simplification of everything being on a ground level. I put the hotspot on the bottom-right-front corner of the box. You should have consistency for where the hotspot is placed otherwise it can become very complicated indeed. Next do some measurements on your box, particularly just measure the top face of the box. I measured it as 308x108. Put the player and box in a family and now we can make the "for each ordered expression".
For that I used the formula of a line:
y-y0 = m *(x-x0)
The idea I came up with is from that formula is as follows.
<img src="https://dl.dropboxusercontent.com/u/5426011/examples20/iso_idea.png" border="0">
Looking at a screenshot I drew a bold red line on each box from the bottom-left-back corner to the bottom-right-front corner. Notice they are all parallel. Next I extended lines to the left and I also made a line from the player using the same slope as the other lines. The y order of where the lines hit the left is the same order they can be sorted. So all that's left is to calculate where the lines will hit.
First we rework the formula to solve for y0 when x0 is 0. This is where the line meets the left.
y0=y-m*x
Then we can calculate m (or the slope) from the measurements. The definition of slope is rise/run or (change in y)/(change in x).
So...
m=108/308
and our formula is now:
y0=y-(108/308)*x
Finally make an event as follows:
For each Family1 ordered by Family1.Y-(108/308)*Family1.x ascendeing
--- Family1 move to top
Example capx:
https://dl.dropboxusercontent.com/u/5426011/examples20/iso_test.capx