I think this MIGHT work, but the real question is what happens to the WDW tickets. I assumed the same as you - if I added
travel insurance, then cancelled the trip, I would get a voucher for the full trip amount minus the cost of
trip insurance and minus the cost of the WDW ticket. Since the WDW ticket is nonrefundable, I assumed I would keep the WDW ticket instead. But, when I asked the rep, she said the cost of the WDW ticket would be added to the voucher, too. I didn't push her on it because I don't really care either way, and I still think she might have given me the wrong information.
My WDW ticket is supposed to be delivered by email 30 days before my trip, since I'm staying offsite. It's 60 days if it's an onsite visit. I wonder if maybe the ticket would be refunded if trip is cancelled before the ticket is delivered? Not really sure.
One other question - does the $681 include flights for all 4 people? I'm not sure if you can buy more WDW tickets than you have flights. They attached my WDW ticket specifically to DD5 on the reservation.