Blossom end blues

[Lycopersica]

I'm growing opalka plum tomatoes. Although the plants have been fruiting like crazy, at least two thirds of the fruit have blossom end rot. Based on a soil test, I know my soil was very calcium deficient when I started. I mixed in compost, Dr. Earth's rock phosphate (containing calcium phosphate) and egg shells when I planted but I guess that wasn't enough.

A week or two ago, when I noticed how widespread the blossom end rot was, I added more egg shell bits and rock phosphate. Then, I mulched the bed with composted leaves and pine needles to keep the soil more evenly moist. I've been careful to water more consistently too. Nonetheless, I noticed today that the newer juvenile tomatoes are starting to get soft spots on their blossom ends.

The plants are showing early signs of over-feeding so I don't want to amend the soil any further. Should I try one of those calcium sprays or give it more time? Am I doomed to sad mushy half-tomatoes all season?