We're going through a similar issue where DS has ben suffering from separation anxiety ever since DD was born 2 weeks ago...I think the fact that he woke up to find mum and dad gone (but his favourite uncle there when he woke up!) the morning of the birth really affected him.

Currently DH is sleeping on a trundle bed in DS' room but we're looking for solutions as well.

We've tried CIO but didn't work...once things settle down we might try one of the gentle withdrawal techniques - which I've seen on thesleepstore website.

Best of luck. Hope you find a breakthrough soon.