Include xml in-memory document to another

I need, with libxml2 or libxslt2, to attach one stylesheet to another. Problem is, this document should be in-memory, not in file. Program is Linux specify. If there's no such routines in libxml2/libxslt2, maybe use Linux-related possibilities, like opening memory and pass fd to libxml2? Problem is: I need to save up memory and to not load file from hard disk, because this stylesheet will include internal capabilities.