[Plugin: TDO Mini Forms] Custom fields not getting appended to the post content

I’m using custom fields with “Append to Post Content” option enabled because I need all the fields to get appended to my post and get them displayed as if they were part of the post content field. If I enter a value into those fields, they get appended without problems, but when I leave those fields untouched in the form, they do not get appended, as if the custom field did not exist at all. But I need to at least display the field %%TITLE%% because I want other users to be able to see that the user that made that post did not actually enter anything into that field, and I want to make it evident.

Is there a way to force those fields to get appended even if you leave them untouched when submitting the form?

Thanks!