Left: Official DRC in place, 6/6/12 (>=6 annular rings)
Right: Adjusted rules, 6/4/12 (4mil annular rings)
For the real boards I only reduced the specs where necessary, under the BGA part. The rest of the board met the requirements. Here's what I ended up with (success!)
All of the 10 were OK for the BGA part (some better than others), but weirdly 3 were unusable in other (in-spec) areas because of drill alignment problems. Even though I only went for HASL finish and had never previously soldered a BGA part, it went straight on and works fine. Not really sure what all the fuss is about! People complain about the fact you need an xray to check for faults... but these things have boundary scan... I mean that's what JTAG was invented for, right?