Emily was up at 4.30 this morning....she goes through phases of this for a week or so every few months.
She is always in bed at 7pm every night.
If she wakes up at an ungodly hour, one of us takes her downstairs (in the dark) and we pull a blanket and foam mattress out from behind the couch and lie down. The house remains dark and the tv stays off. No bottle (she isn't hungry that's not the problem). She soon realises that there will be no fun and games so she'll lie down on the mattress with DH or me, crawl under the blanket and go back to sleep.
This works about 90% of the time and we can usually get until 6am out of her this way
Good luck - it's the flipside I guess of having a child that goes to bed early (and I LOVE that...I'd rather early mornings than have her up half the night!)