Automatically leave large blocks of positve feedback to your buyers over the 80 character limit
Yes there is an option on your online eBay account to automatically leave feedback. It's under 'My eBay' => 'Account' => 'Selling preferences' >= 'Automate feedback':
This only allows you to enter feedback comments up to 80 characters. In some cases you might want to submit up to 200 characters like you can if you manually leave feedback.
Setting up Jumble Saler to leave feedback instead
Click on the 'eBay accounts' option on the Jumble Saler main menu, then double click one of your eBay accounts from the list. Then use the 'Automate feedback' tab:
to specify your feedback to me left for that account, and save.
Once you have done this, then every time you retrieve your orders in Jumble Saler, feedback will automatically be left.