between + and - of the bridge output?
Doable, but not as good.
You can check out the staged regulator designs (pre-regulators) from Walter Jung. If that's too much, get a resistor or zener from Radioshack + another LM317/78xx series regulators and use the resistor / zener to raise the ground pin's potential, and then use the 2nd regulator to step it down further. A typical approach in LM317 datasheet to expand the (input) voltage range.