Sweet, I just figured out the other half of this. It seems obvious looking back, but I didn’t catch it when I was setting it up.
You make your own chunk and give it a name. E.g. I made a chunk called yui.OuterTpl that contained this:
<ul class="yui-nav">
[+wf.wrapper+]
</ul>
And then when I called Wayfinder in my template, I just referenced the name of that chunk in the outerTpl variable. So here’s what my call to the Wayfinder snippet looks like:
[!Wayfinder?startId=`0` &level=`1` &hereClass=`selected` &outerTpl=`yui.OuterTpl` !]
I’m off to update the wiki...