I've made a remote control profile which allow my Sony K700i to control media center via bluetooth, maybe it may work with other Sony phones.
Here's a the screenshot:
(http://perso.cvp-net.com/misc/MediaCenter.gif)
To use it, just upload this file (via bluetooth) to your phone: http://perso.cvp-net.com/misc/MediaCenter.hid (http://perso.cvp-net.com/misc/MediaCenter.hid)
(software used to do this is here: K700 remote Profiler (http://www.softpedia.com/get/Mobile-Phone-Tools/Sony-Ericsson/K700-Remote-Profiler.shtml))