non standard key signature question

[corallina]

I am working through a guitar book based on middle eastern forms
the author uses a key signature for the example modes which is
a combination of two flats  (key b flat) and one sharp (key g)

Is it possible to set up a key signature as above?
I do realize that I could simply set up a key signature of either
b flat or  g  and then just add sharps or flats as necessary
but thought to ask this question as a cursory search come
up with nothing.



patrick


In case anyone is curious the book is  the alfred  guitar atlas series
on the middle east and the author is  jeff peretz