Prevent enter key from submitting text entry for evaluation

I'm running into a slightly different version of this problem. We present learners with a sentence that has no punctuation and ask them to type the whole sentence into the text entry field with correct punctuation. Some sentences are long enough to need two lines, so we make the text boxes tall enough for that. They are allowed 2 attempts. There is a custom submit button on the slide with a trigger to submit the interaction when user clicks submit button.

If learner enters text and presses submit, all is well.

However, if learner enters text and hits ENTER out of habit, that submits the interaction.

The problem is that the ENTER also registers as a linebreak so even if they enter the correct answer, the extra line break makes the answer register as incorrect. When they go back for their second attempt, the linebreak is still there and very easy to miss, so the learner can easily still get the incorrect feedback layer just because they have a linebreak at the end of their answer.

So we need Storyline to either interpret ENTER = submit or ENTER = text entry, but not both at the same time.