Thanks to Niall for the following.
I’m in Melbourne Australia and in our State Newspaper the Herald Sun they had an interview with an Australian actor called Grant Bowler. This interviewed confirmed that he had a guest role in the Season 4 of LOST but that was all that was said. The Herald Sun is Australia’s most popular newspaper so this is very reliable but I understand if you wish to publish this in the Rumours Section of your site. It did not publish any details of the character’s name so it may not be worth mentioning at all. Being an Australian actor it may indicate a “flash back” set in Australia for any character or a “flash forward” for Claire once she gets back home? Anyway, here is Grant Bowler’s imdb page (click here)
Source: Herald Sun