We do not provide the OpenURL argument for Endnote because:
An alternative to OpenURL is Endnote Click. See this article on Endnote Support's Knowlege Base.
We tested the free version of Endnote Click that give you a limited cloud storage space. It works well with NUS' proxy bookmarklet to obtain full-text from PubMed and Web of Science, and we encourage you to explore.
However, as we have not been able to test how effective Endnote Click is with all our subscribed databases, we cannot guarantee that it's the best thing since sliced bread. Please contact me if you encounter issues in your exploration. :)