Notes having two values contemporaneously

[Die5Willes]

Hello!
I'm trying to type a piece by Robert Schumann: "Des Abends" (Evening) from the 
Phantasiestücke op. 12 for piano solo. The time-signature is 2/8 (no mistake!!) 
and the right hand plays tuplets in 16th-notes for almost the entire piece. So 
there are two tuplets a measure with stems down but they are printed in a 
manner that every second note is not only a 16th-note but at the same time an 
8th-note with stem UP!

Does anybody know how to do that?
I'm using lily 2.2.5 on a windows-operated machine.

Thank you very much
cu
Stefan