Eventually got a reply from aib. It seems that once the policy has been set it cannot be changed. We had decided on the 50/50 split ourselves at the time, it seem the most practical.
We did have a claim lasting 60 days back in feb/mar 07 due to illness (him - cut tendon in finger, cooking accident!) so that seems to rule us out for transferring to a new policy with someone else and not having waiting period.