I dislike the idea of making a point to use such rigidly isometric sprites for dwarves and other characters, and I think pursuing that art direction is a significant mistake that seriously misunderstands the purpose of its use in the games that use it. This is not an art style that is intended for use in a game like Dwarf Fortress. If you ignore this fact, rather than being simply icons abstractly representing the position of characters, your characters will suddenly appear to actually be walking backwards and sideways down halls, and everyone will be looking off to one side together.
Before mimicking the styles of the games cited in this thread that used isometric sprites, note that every one of them not only had character facing, but had walk animations to provide dynamic posing. Not one of them would have used the same art direction if they didn't. Indeed, the oft-cited mock-up of an isometric DF that soup cites wisely avoids using isometric sprites, despite the way the terrain is rendered:
This use of non-isometric sprites and iconic poses is not ugly, and it is not a shortcut. It is smart design. It takes into account that units in Dwarf Fortress have no facing and will not be animating out of a default pose.
That doesn't mean you can't have your dwarves looking to the side. It doesn't mean you can't respect the fact that the world is isometric when drawing them. Let me give you an example of a game that better represents the sort of situation Stonesense is in:
This is the open source game Battle for Wesnoth. They have larger sprites than the 32x32 ones you're working with here, but that's not the point -- the point is their stylistic approach, which uses dynamic poses and vague, indeterminate facing, while still having clear isometric aspects, despite the game not even using a true isometric environment.
Unlike Super Mario RPG, Wesnoth takes place on a hex grid and supports only two displayed facings: left and right. These have no gameplay impact and are just a horizontal sprite flip. Characters have no walk cycles, only one frame attack animations, and yet must look engaging and dynamic. Despite these restrictions, Stonesense is even more limited in what it can display than Wesnoth is. I strongly recommend, therefore, that you carefully consider how you pose these characters, and take their hint: Your sprites will look much better to a casual viewer if you do not line them up in a default pose with a clear facing, as if they were waiting to be rotated and animated.