I think that message is displayed bu the "ShowMessage" function. If you open the quiz's HTML file in a browser you can change that function to do something differnt to what it normally does.
Also, in the latest version of TaskChain I have added a new output format for JQuiz, called "JQuiz (v6) from xml (Intro)". It is intended for the situation you describe in which you want to use a JQuiz to introduce the chain. You can select this output format from the task settings screen within Moodle (see screenshot).
I originally created this output format so that you can use a JQuiz at the head of chain to ask a question thus:
You set up the JQuiz so that each answer is "correct" but the scores are "60%", "80%" and "100%" respectively. Then you can use the post-conditions on the JQuiz task to branch to the appropriate next task within the TaskChain.
In your case, you only need one button, so it can say something like, "Click here to continue".