[phenixbb] RNA 5' end needs 2 PO4s

I'm trying to model the first residue of an RNA, which has a di (maybe tri) phosphate on the 5' end I'm sure someone has already worked this out ... should we call the 1st residue GDP or GTP, and somehow tell phenix about the bond to residue #2 (how?) or should we add pyrophosphate to the default 5' phosphate? PS - as a side point, elbow generates GMP with no phosphate thanks, Phoebe