The problem is that it would require us to enable the Search All Forums function, and then hack its functionality as well as the overall FT display scripts.
We disabled the Search All Forums functionality a while back since it causes a pretty significant drain on our server. This is caused by the way UBB stores data and then accesses it through the search.
We understand the usefulness of being able to search all forums at once (There have been plenty of times I could have used it for admin reasons

), but due to the immense amount of postings, high traffic, and a currently overloaded server, we removed that option.
We are currently working with a new hosting company to move some of our other sites off, and give FT a little more breathing room. When we have everything back in place, we'll be better able to determine if we can turn the Search All back on without it impacting performance.