Airport express and some third party software to make it a normal sound device, but you will get laaaaaaag.
Otherwise get a FM transmitter in there - no lag but rather poor audio. 2.4GHz video senders will mess up your wireless lan, bluetooth is too short range and has lag, There are some 900MHz solutions for video senders, but again, that's analog so going to get interference
There are also some digital audio links that have minimal lag which would be ok, but they are hard to find among the see of 2.4ghz analog junk.