I do them like this....
I set up two text styles, one set at 30 degree rotation and the other -30. And make two dimstyles for each of those textstyles. I usually name them dimiso and dimiso2.
I draw a dimension using 'aligned dimension'.
I use dimedit, oblique (O) command, and select the aligned dimension, and play around with the angle.
It's usually 30, 90, -90 or -30....I just try those and one usually comes out the correct way....then I'll change the dimstyle to the one that shows the text the correct way.
It's probably not the correct way...but it's the only way I know how to do it.