It would require a completely new drawing for the lower horizon piece.
Sup, Ryu. Actually, with forms this basic, I think breaking the image up into 3 parts - left side of street, right side of street, and middle area, then moving/transforming (in Photoshop) each part could be a quick fix. Left and right sides would get a skew transform, and the middle could simply be moved down. Vertical lines would stay vertical, and horizontal lines' angles would all change. *places hat overturned on ground and waits for quarters*
Just make sure you end up with something you like. Looking at your rough-ins so far, they don't seem to have any sort of focal point. Rather, all the viewer's eye gets to do is wander around the different buildings, because the center is just blank, flat street.
So, after all the work you do rendering, just make sure your end-result is effective.
How many times have I completed a detailed image only to sit back at the very end and be like, 'Ok . . . wait, this is pretty boring' . . . I got caught up in the details.