Wow, what an old post!
Oddly I just sent MM tech support that suggestion. I have little hope for it, in spite of the overwhelming surge of mass media popularity serious maqam performance is enjoying these days. (Oh, wait that was a dream I had the other night)
I have been thinking about this stuff the past few days - first off key sigs for maqams and modal musics are hardly standard. How would you make a key sig for Saba, for example? You need Bb, E (sikah) "half flat" Gb and sometimes Db at the top of the octave, sometimes not. Modes frequently have rules about the pitches above and below the the melody's main octave. Should that be in the key sig?
Second, those pitches aren't really 1/2 flats, but slightly different, and it depends on who is playing. the E in Bayati is lower than the E in Rast, so to notate them you would need two symbols, and to play it back you would need the right intonation.
It might make more sense to simply type the name of the maqam at the point on the page where it comes in than to have a key sig.
Or, for the key sig, the quick way is to just use expressions. This way you can get it to look exactly right. But if you want to have playback work properly that's not enough. You still have to have some method of raising and lowering equal tempered pitches.
I have been asking for an interface that allows users to start with a blank staff and drag from a pallet of accidentals to where they need to go on the staff, then for the 1/2 flats and 1/2 sharps we should get to define how many cents above or below western tuning they are.
Finale already can do what you are asking for, albeit by a different method.
Create expressions with pitchbend, and then a non-printing expression with a zero value for pitchbend. Assign metatools to your microtonal flats and/or sharps and now you have a one-click way to insert "quartertones".
Then, if you are feeling adventurous, copy a measure you assign said expressions to. Copy it to a clip file (opt or alt-C). Then when you want to use it paste it from the clip file with the Edit Filter activated and only "expressions..." checked. Admittedly clunky, but it does work. In Finale 2012 this is working better than in 2009, for whatever reason (my own perception possibly, or advances in the Aria player for GPO4.)
See you over at the other forum,