Westreamu have developed an open method for adding sign language interpretation from a remote location to livecasts as well as web video streamed on demand. For a technical desicription of how this is done, using chromakey technology, please see the wiki article Remote sign language interpretation in live video productions.
Westreamu have used this method on numerous occations, both for our original productions as well as livecasts produced by other companies. Swedish national broadcaster TV4 have also chosen this method to increase the accessability for a number of their own shows.
As a demo, and visual explanation, embedded below is a 10 minute clip with the live produced sign interpreters and recorded closed captions (cut from the full presentation in Swedish). Warning! You might get confused from the relation in time between what I say and what you see (video/text/signs). This is an effect from a live demonstration of the livecasts that is the demonstration. and somewhat delayed due to the way video streaming works.