Subtitles (iTunes Timed Text)

Apologies if this is a daft question but have been hunting for an hour to no avail.

I have a series of SRT subtitle files that play perfectly as soft selectable subtitles in Quicktime, VLC etc. However, I need to convert them to the .ITT format for delivery to a client and none of the subtitling software I have seems to have it as an export format and I can't find any convertors.

Am I missing something? Is it simply a file extension rename, or export to XML then rename it? I can't add it as a closed caption option in Compressor either and, even if I did, what format will that throw out?

Any help would be appreciated.