The correct controller for switching intervals on G# and A is cc#15, not cc#16.
Here's the info from p. 41 of the GPO manual:
Hidden Playable Trills/Wider Interval Tremolo Controller CC# 15
The Solo keyswitch strings use cc#15 to control an alternative switching system for trills on keyswitch notes G# and A. The standard keyswitches (G# thru B) give the user control over half-step and whole-step trills plus their muted counterparts. The cc#15 controller extends switching to intervals from a half-step to as wide as a major third using the following values:
0-32 = half step
33-64 = whole step
65=96 = minor third
97-127 = major third