Double-clicking the StrokesPlus taskbar icon toggles whether StrokesPlus is disabled?
Of course, you can always create a gesture which calls acDisable() in Lua script, or acDisableNext() to disable only the next mouse down capture (after the next mouse down, gestures will happen as normal).
Umm, actually by complete coincidence (not intention) calling acDisable() again will enable S+.
acDisable() actually posts the message to S+ as if you clicked the Disable StrokesPlus item in the tray menu. So calling it again, posts the message again...which toggles the state back to enabled.