You don't have to select a gesture. You can leave the gesture dropdown blank and select modifiers only.
For example, if you have the right button assigned as your draw gesture (hook) button and select Left button as a modifier, the action would fire if you pressed the right button, then the left button (and let go of both [sequence irrelevant as long as hook button is pressed first]).
It would be great if could be possible to assign gesture actions without stroke key pressed (optionally). For example, in "Just Gestures" its possible to make gesture form volume up/down width left button pressed and mouse wheel, in the same time having stroke button set as right mouse key. I think this kind of functionality would be VERY useful for a lot of people.