I have recently shared a post on using the heartofPluto separation in Ayab to knit a DBJ 3 color sample where each color was not represented in each row, with each color knitting a single height. Img2 track at this time does not offer a built-in similar option. There is a FB thread going on at the moment on this topic that can be followed there, Tanya Cunningham has shared a document on this topic. I am using the same repeat as in my Ayab tests, 
with my color changer in this threading sequence throughout
The import into img2track shown here for the traditional 3 colors per row setup,
where normally each color in each design row knits twice. Because selection occurs for pairs of rows, the first preselection row is from right to left. To decrease the backing rows, the ribber is set for birdseye. I prefer to have an end needle on each end on the ribber, keeping in mind that the total number of needles in use there needs to be even. The machine provides reminders as to which color should be knitting. My samples are knit using KCI on the top bed. Because the preselection happens twice, it is easy enough to knit in pattern from left to right, 
when the carriages have reached the right side, simply use a ribber comb to push all needles back to B. 
The next color to be used is preselected as the carriages travel back to the left, change color when on left, and repeat.
It is easy enough to develop a rhythm. I used to tell students some things are made easier if one develops a tune to play in one’s head as a series of actions. Here I found myself thinking “knit to right, erase (selection), knit to left”. I had tension yarn issues on the right which explain some of the issues on the side edges and changed color 1 to blue for increased contrast. The proof of concept: 
Speeding things up with color separation, beginning with the method that will have each color, each design row knitting twice. The repeat is 10 rows high, so it is expanded X6 to 10 by 60 rows. In the final result, the second row for each color in the separation is in turn erased. The red was added to make all 3 colors visible while working the separation, avoiding confusion with the white ground. The knittable result as usual is in a black and white png 
The img2track settings are for now for 2 color knitting, the prompts for the color changes are lost.
The color-changing sequence used was still 1, 2, 3. The design with a birdseye backing 
The ribber can also be set to knit every row, resulting in elongation on the knit side, while creating an interesting striper backing
Comparing this version to the birdseye backed one for repeat height 
Comparisons: HoP, pushing back needles to B, and color separation results. In the latter, the design is likely elongated in part due to a change in the distribution of thinner yarns to larger design areas with no tension adjustments 