Basically what you need to do is download Fluid app:
Download a Transmission icon (it does not have to be an .icns)
I used 256x256 px png on iconspedia:
In the Fluid app, set the URL to your Transmission url (e.g.: my_worldbook.example.com:9091), name it (e.g.: Transmission), set the desired destination for the app (default: Applications) and for the icon use the image you previously downloaded.
Finally click "Create".
If you want to have a menu bar application then launch your newly created Transmission app and on the app menu click on "Convert to MenuExtra SSB…"