Request custom validation (instead of enforced validation)

Dear all,
I want to equip a Constant Sum Question (type: Choices, options: Total Box) with the "Must Total" validation. Typically, the validation is enforced. This means I can only submit responses that satisfy the must total criterion.
Is there a way to only request a valid response? That is, participants who enter an invalid response are kindly asked to reconsider their response but can nevertheless continue with the survey if they wish to do so. This would be the analogue of the "request response" feature.
I'm grateful for any suggestions.
Best,
Peter