I guess the easiest thing would be to create a new reference type in Endnote and a foodnote template matching it in the Science output style, with only the field holding your intended text. Changes or additions to reference types are done thru the edit preferences, reference type, modify options in endnote. (and are specific to the computer but can be exported and imported into endnote on other computers). Now enter a new record using the new reference template. Insert that record into your document's footnote (it won't necessary look right, yet, so you can wait to do this until after the next step). Next change the Science output style thru the Edit>Output Styles> Edit output style "Science", go to the footnote templates, and add the new ref type to the templates. Insert the new field from the dropdowns into the blank template for that ref type. Save AS to a new name and use this new output style to format your document.