I want to set piped default answers for a Constant Sum question that are not a valid answer

I have a series of Constant Sum questions that ask people to make allocations with different budgets. I.e., first with $1,000, then with $800. I used piped text and default answers to populate responses from the $1,000 question into the $800 question, so that respondents have a jumping-off point to start from. However, because those answers aren't a "valid" response (they exceed the custom validation total of $800), it doesn't work properly. The first two allocation categories get erased so that the total equals $800.
Is there a way to set it so that the validation doesn't let them proceed with responses that are "invalid," but allows them at least temporarily before the answer is submitted?