I don't think you'd actually use a Dingle / Double Crank set up for spur of the moment changes, like riding along and suddenly thinking "Gee, maybe I'll stop and go from big/small to small/big".

The Dingle is sized so the jump is on the order of a 1/4" change in chain length if I remember correctly.

If your riding in a scenario where you'd actually contemplate that radical a change, say on tour, then carrying a chain-breaker isn't an unrealistic expectation. Or an entire chain sized appropriately.