A commonly said rule on photography is to isolate your subject; such that your subject stands out and there are no other distracting elements.
I personally feel that there are no rules on photography although few of them could be used to take better photographs (as long as you know the rule and why you are bending or breaking the rule).
Adding subjects of secondary interest could give a different dimension to portrait photography. This is slowly catching up and several advertisement photography uses this to a larger extend. Though in advertising photography, the difference being secondary subject is as prominent as the primary subject.
Depending upon the location, you can choose suitable secondary subjects. It could be a flower, a veil, a hair drier, balloons or even cityscape.
Try what you are comfortable with. You may even use a larger aperture of F/10 or F/12 for portraits with cityscape.