I have not been able to test this, but what I can do is to frame the question in a way that points to what seems to me to be the crux of the matter...
Saving the current entry "card" is trivial in that Memento takes care of that when the checkmark is pressed. The sticking point is to then automatically display a blank card for addition of a new entry. One could contemplate setting up a trigger on the of Saving the entry running a script that would run After saving the entry.
But, as far as I can see, there is no way for the trigger script to initiate the addition of the new entry.