I also am curious, as I'd like to add my plugins, but so far they have their own make files. I was told to get on IRC and talk it out, but I haven't gotten to it yet, so a tutorial may be a more convenient option :-)
From: Lex Trotman <elextr@gmail.com>
To: Geany development list <devel@lists.geany.org>
Sent: Friday, June 7, 2013 11:51 PM
Subject: [Geany-Devel] Adding a plugin