Looking at page 119 in my manual on External Scale Editing we could just use a similar process for the global (grid) scale.
Arming for external scale edit:
Hold GRID and press REC then enter scale mode by pressing SCALE SEL
Editing current scale:
Current scale is determined by incoming midi ‘chords’.
eg if you press C3, F2, A4, all notes generated (that aren’t fixed by specific page scales) will be C, F and A in their respective octaves (their respective programmed ones, not the keyed ones – perhaps we have the first key of the ‘chord’ determining the base octave of the transposition relative to octave 3 eg C3 would give no base octave transposition but C4 would shift everything up an octave etc)
Letting go of all keys in the ‘chord’ essentially fixes the current scale. Any new key presses will start a new scale and instantly clear the previous one.
Press REC again or SCALE SEL again
What do you think Garbiel? I could generate some example tables of what I mean if you like when i get chance?