Nope, this isn't yet supported, although it's certainly been discussed
-- Bruce was first to raise it as a development issue, I think.
 a) B. M. Trost, Chem. Eur. J. 1998, 4, 2405–2412; b) H. J. Ache, Angew. Chem. 1989,101, 1–21; Angew. Chem. Int. Ed. Engl. 1989, 28, 1–20; c) H. Frey, Angew. Chem. 1998, 110, 2313–2318; Angew. Chem. Int. Ed. 1998, 37, 2193–2197.
Here 1b) consists of two collapsed cites, and basically we have two (!) additional hierarchical levels in the bibliography. Instead of one item per bibliographic entry, each entry can contain one or more collections of cites, and each collection can contain one or more cites.