How can I suggest annotations in Seq2Seq tasks?

In a Seq2Seq annotation task, I want to suggest target sequences that the annotator may choose from or modify. The target sequences depend only on the source sentence and can be hard-coded in advance.

The demos (Translation and Text to SQL) provide such suggestions. How can I add this functionality to my own project? I searched the settings, tutorials and Stackoverflow, but couldn't find the answer.

Thank you for providing a great, easy-to-use annotation framework, and also for any help in this matter.