Well not impossible actually, but the highly desirable (for biblical scholars) and unexpected, Zotero add-in that "does" SBL stylesheet citations and bibliography. There is a bug using the style with version 1.0.3 as Mark noted in his post Zotero: SBL style beta now available it crashes if you try to add a page number to the footnote :( However, it is said to work with the Beta version 1.0.4 of Zotero, so not long to wait...