Well, you can get reflectors that you can hand-hold yourself, if your camera is on a tripod. Or you can get a "magic arm" (a flexible or hinged/ball-jointed arm with clamps on both ends) that will hold on to your tripod leg with one clamp and the reflector with the other.

http://www.bhphotovideo.com/c/produc...ip_8_in_1.html

http://www.bhphotovideo.com/c/produc...ver_White.html

http://www.bhphotovideo.com/c/produc...ion_Magic.html