even though it's been postponed to CSS4, iOS does support pointer-events property, so this is pretty hack-y, but may get the job done:
Code:
<li><a class="no-link">Chapter 4</a></li>
with
Code:
.no-link { pointer-events: none; }
not a great solution, though.
apple's asset guide actually states that they auto-generate samples so that you don't have to do that, though, unless you're making a read-aloud book, in which case you have to provide them with a separate sample epub.