Assuming OP means MQM and that's a typo. Amex MilesBoost does NOT award any Delta MQDs (Medallion Qualifying *Dollars*).
For that big of a swing, I would not be comfortable doing what OP is thinking. It's one thing if you have $50 or even $500 refunded in early January, and the quickly spend it again (e.g. before your statement cycle closes). $7k is...a different story.
If you really need those MQMs, is there anything you can go ahead and pay in advance perhaps? A large tax bill, annual insurance, work expenses, etc.? You could also overpay a few utility bills - generally if you do that your account will just carry a credit that gets consumed over the next couple months (though I don't know if they'd force you to take a refund if the credit amount is that large).
Perhaps you have or know of a kid in their late teens/early 20s who needs a nice, new-to-them car?
If all else fails, I can send you what's left of my Christmas list, plus some extra stuff I've had my eye on for the house. I'll even let you pay express shipping for much of it. Of course, I'd be doing you a favor and would consider that my in kind reimbursement to you for those purchases.
