Hi,
You can make a custom html page and you create wcf services that makes the process in Trello.And you can call this webservices from the html page.
Also if you do not want to create a custom page , you can create a ribbon button , in this button you can trigger Crm Plugin and you can call the wcf services that makes the process in Trello in Crm Plugin.
Polat Aydın Crm Software Developer