I appealed to Julie Zickefoose last night via email for help with my beer box/bluebird problems. She came through, as I knew she would. And here's what she had to say:
No way to baffle a box on a fence. You've learned a real good lesson. They'll always outsmart you! and will do the worst thing, the one you least want them to do... Yes, they will accept a box placed right next to the one they're using. I would put the same box (not a strange one) with its contents intact on a baffled pole RIGHT NEXT to where it is now. When they enter that (and it should take only five or ten minutes,) let them settle down for awhile, and then move the whole affair another couple of feet away from the fence. Then repeat, another couple of feet...until they're safe. You have to get it far enough away so a snake couldn't loop over from the fence to the pole.
Remove the eggs and nest while you're messing with the box, and only replace them when you've got the box securely mounted. Once they have accepted the new LOCATION, give them a day or two and THEN put the nest in a safer box on the same baffled pole. You should be good to go. The change of location is a bigger deal for them than the change of box. Try to get a box that's similar to the one you're replacing, of course.
IMPORTANT: She has to have been incubating those eggs for at least four or five days for you to pull this off. DO NOT ATTEMPT this if she hasn't started incubation!
GOOD LUCK and let me know how it goes!
Good grief...what have I done????
So now I wait for Mrs. Bluebird to start sitting so I can try to save them from my dumbness.