Syntax highlighting markdown code blocks in Jekyll (without using liquid tags)
Fenced blocks were introduced with Redcarpet 2. Jekyll now supports Redcarpet 2.
As an aside I am using Redcarpet with Rouge until Kramdown support is available.
In addition some people prefer Nanoc to Jekyll.
Alternate solution
Markdown allows HTML, so if you don't mind adding a bit of JS, you could do this:
## A section
Here is some Ruby code.
<pre>
<code class="ruby">
puts "hello"
</code>
</pre>
Then you could use Highlight.js (documentation here) to add highlighting based on that class.
It's not an ideal solution, but it should work with any Markdown parser.