I've made you a modified version of the FTP Upload destination that uploads with FTP and then shortens the URL with bit.ly like you say - download it from the link below:
http://aptonic.com/getdestination.php?n … y.dropzone
Before you double click on this destination to install it, you'll need to edit it with a text editor (TextEdit should work) and update the following two lines at the top:
$BITLY_USERNAME = "your-bitly-username"
$BITLY_API_KEY = "your-bitly-apikey"
You need to change your-bitly-username and your-bitly-apikey to the info you get from bit.ly when you create an account. Then save the file, double click on the script to install it and put in your FTP details as normal.