Well, lucky me! When I went to the store today, I actually found that they had in stock a pre-flared, pre-fitting'd bridge line that was just the right size!
So I bent that into shape as well as I could and screwed it in tight. Tomorrow I'll repressurize the system and we'll see if the leak has been slain - or if it has managed somehow to survive.
Great lead on tubing, Sirrotica. When I've done all that needs doing with this project I think I'll make a list of all the places I bought things and what they were, so y'all can have the benefit of my experience (and stinginess) when looking for pieces and prices.