Please read this carefully as it is not what you might be expecting.
I'm building my site in a development sub domain. I don't want to have to go through the complications of running find and replace plugins after moving the site to the live area (as this can often go wrong on some serialized data).
I want to enter the urls into pages as they're going to be on the live site (they need to be absolute URLs for the RSS feeds. So I need a method with PHP or Javascript to find and replace http://mysite.com with http://dev.mysite.com on the output pages. This way I can still test and preview the site and when it comes to going live I just have to uncomment that code. I'm not worried about the URL in the settings as that is always easy to change.
I hope that makes sense.
Thanks.