Hmmm...I think you might be better served by asking this sort of question of the Davidson staff. They're very helpful.
I do have one suggestion (good for anyone thinking of a portfolio): videos! Be very selective about what you choose. Hours of cute kid vids won't cut it. But I have a theory that if you see a DYS kid in action, you know it. It tells you more than any worksheet or parent-told story can demonstrate. If I were putting together a portfolio, a handful of very short videos taking up just a few minutes of the reviewers' time (5-10 minutes, TOPS!) would be the spine of my presentation.
And remember, you're trying to distinguish between an MG or even HG child and an HG+/PG child, not merely that he's GT. Big difference! You need to show that your child is 3+ grades above age-level (and more would be preferable, especially if you are trying to get in without scores).
I don't mean to sound negative, but I really do think the usual DYS response to lower scores--even with a good portfolio--is a flat "no." They get enough applicants who have the scores that they don't have to accept lower scores. It's tough, since we all know how finicky the testing is, especially at the tails. But it's all they've got, so it's what they use.
My best advice is to make arrangements to retest and start collecting evidence for a future portfolio.
