There is a new policy on shared first authorship for medicine journals. See also the article entitled “A Multi-Journal Partnership to Highlight Joint First-Authors of Manuscripts” published simultaneously in the February 2015 issues of the 5 journals (listed alphabetically): Gastroenterology, Gastrointestinal Endoscopy, Gut, Journal of Hepatology, and Hepatology.
Is there a possibility to incorporate this in your reference program?
For your understanding I would like to highlight that the issue is not an individual problem but something a lot of people will face using your reference program, since these are requirements for all authors that plan to submit an article to any of these journals. Ideally, the EndNote program would develop an additional option in the reference program where you can specify which of the authors are joint first-authors if applicable.