Paddling for over 1/0th of a mile is definitely a no-go with a DS. I don't know whether it's just the non-ideal paddling position or also the fact that the DS hull isn't as easily driven as a kayak or row boat. There are several people who have experimented with oars. They are challenging to stow for anyone who doesn't have one of the '60s DS 1s, because the bulkhead (or in the oldest models the transom tank) limit the maximum length that can be stored in the cockpit.
I've sailed on a friends DSII that was fitted out with oars. I used them inside a marina, once. It worked, but I don't recall looking forward to longer distances. But, as he would have admitted himself, his were a foot or two too short, because of the need to stow them when not in use. So, longer oars might have made the experience a bit more efficient. Who knows.
But that's a reason I'm curious to learn how this works out for you. Is the DS hull inherently limited for human powered propulsion, or is it just a matter of finding the right technique.
PS: one thing I've had reason to try recently is paddling with motor assist. Like an e-bike

. We had an ambitious itinerary (over 8nm point to point) and we ran into repeated calm patches. We had a young eager crew that hated sitting around, so we let them have the paddles. At the same time, we put the motor on some low power setting. That combination worked really well. It was easy to keep the boat at a speed where paddling was efficient, and the paddling helped extend the range. Already, the motor has much longer range at lower speeds, so we could have kept that up well beyond our typical 3 or 4nm of motoring range. (Or until the first crew strike)