But DON'T...
Don't cut your plant in half...isn't it outdoors...if it is there are no space limitations cause at this time of year that plant isn't going to get that much bigger!
If you want the secondary growth to start growing all you have to do is cut the top node off so the 2 branches directly below it start growing as your new tops and the rest of the branches will grow quickly while top is stunted...you can get the same effect by tying the top down below the top of the plant...this releases a hormone that makes the side branches grow because the top is no longer at the top, the plant needs a new top.