ok, Now I saw this post... For some stupid reason I've missed the whole time
Thank you for your input!
I suppose that a system based on sprites that have frames which are referencing different points of view of an object and it's related on the distance from the center of the screen, could make up for a simple pseudo 3d effect. A simple example,
-if object is on the right side of the screen-> display frame 2 (object as seen from the left)
-if object is on the center of the screen-> display frame 1 (object as seen from the front)
-if object is on the left side of the screen-> display frame 0 (object as seen from the right)
Adding inbetween frames/points of view will render more fluid results.
I've used a similar method in a test game to fake the movement of the defensive towers. Please, check it out if you don't mind the waiting time (it's 100Mb, not very well optimized) and somewhat lengthy introduction (which can be skipped).