The easiest way is to purchase the content yourself so that you may use the licensed photos in your designs over and over again. Paul Markham's content is affordable and of high enough quality that they can be used easily in designs.
http://www.bargainbasementcontent.com/
A second option is to have the client find photos from the sponsors they will be promoting and use those in the design. As long as the photos are used to support the sponsors' sites, many are okay with the practice.