I love board formed concrete like ol' Corbusier used to do. "Brutalistic" architecture at some of its best. But, you need to make sure that the loads of concrete will handle the new loads.........I assume you have.
Now, to answer your question. Yes, there are light-weight products out there that look like various stone formations. They are 'great' and look 'great' and if properly installed, you cannot tell them from the real thing. You just have to lay them like you would real stone so they look like real stone. The advantages are obvious, and I would look into them. I don't have a web site at this point, but the information is out there.
You could also 'stucco' if you like that approach.
You could also make your own forms, mold the concrete 'outside' the house, and bring in the units and attach them to the wall, or tilt them up or what ever, again assuming there is ample structure to hold it up.
By the way, if you are looking for a way to stain the concrete you can add color to the mix, or stain the surface with iron sulfite, or similar. Iron sulfite "rusts" the surface and you can make the concrete look pretty cool by sprinkling the iron on a wetted surface, cover it with plastic, or just leave it to the weather. The amount of the rust depends on you and the material. I did this to a lintle stone I had sandblasted with a motto, and considering the stone was "too pure" in shape and color, the staining worked great to give it some character.
Have fun. Be careful with the heavy loads you will be dealing with, and let us know how it turns out.