This is still possible but Im not sure what you have done wrong without looking at your code??
A wrappable texture just needs to be a power of 2 on each axis....so a 1024x256 is wrappable! It doesnt need to be the same dimension on both axis
Also take a look at:
SetDefaultWrapU() and SetDefaultWrapV() - set them both to 1
They can work even when the SetImageWrapUV() Functions dont work. Whether they work depends on if your mimapping or not (Have you set SetGenerateMipmaps(1)?? - looks like you have from the smoothness of the graphics - if you havent....just using The default wraps will fix this)
Another option is to load your 800x200 image and simply add the line
ResizeImage(img,1024,256) - then turn wrapping on and it will work fine
If your still struggling after that then a VERY easy shader would fix the issue for you
Heres your graphics wrapped on a non power of 2 sprite image
This is ONE sprite with SetSpriteUVScale(spr,0.33333,1.0) to produce the wrapped effect so it is doable but takes a bit of care.