tuplets in compound meter

[Malte Meyn]

Hi list,

I’m setting Sriabin’s “Vers la flamme” in LilyPond. This piece in 9/8 
contains tuplets where 5 quarter notes replace 9 eights, or 4 and a half 
quarters. But of course I cannot write \tuplet 5/4½ or \tuplet 5/(9/2). 
\tuplet 10/9 won’t help because it prints the numerator 10.

I could do something like
  \tuplet 5/9 \scaleDurations 1/2 { r4 ... }
or
  \tuplet 5/9 { r4*1/2 ... }
but wouldn’t it be nice to have a version of tuplet that works better 
with compound meter? \tuplet 5/4½ is a special example but \tuplet 2/1½ 
is more common (it is often written as \tuplet 2/3 but I’ve seen already 
some editions that follow what Peter calls the “mathematical rule” at 
http://lilypondblog.org/2014/09/how-to-write-readable-tuplets/ strictly).

I don’t have an idea for a good syntax here, any suggestions?

Malte