You should try out the DisguiseCraft plugin for a quick fix. DisguiseCraft is currently available on the Bukkit website. Do keep in mind that it also requires ProtocolLib to function properly, and you will need to have both installed on your server. You may find a link for ProtocolLib through the DisguiseCraft page. I currently use the two on my server and have had no issues with functionality.
If you would prefer a more direct approach however, since you are coding your own plugin, consider looking over the Lib's Disguises Developer API. Like DisguiseCraft, it too requires ProtocolLib, but the source for Lib's is publicly available and is intended to target developers. Just like DisguiseCraft, you may find a link for ProtocolLib through the Lib's page.