According to the developers if Yatse themselves you should be able to accomplish this with the API.
Not sure but you could try to send an intent with Tasker. Try this for playing a movie:
Action: org.leetzone.android.yatsewidget.ACTION_APP_VOICEC OMMAND_PARSER
Extra: org.leetzone.android.yatsewidget.EXTRA_STRING_PARA MS:%avcommnofilter
The %avcommnofilter contains whatever you said after the trigger. Which is 'xbmc' in this case. So the command "xbmc play <movie>" would send org.leetzone.android.yatsewidget.EXTRA_STRING_PARA MS: play <movie> to yatse.
As for play, pause or stop you would use the MEDIA_COMMAND instead of the PARSER.
Let me know if it works. If not, maybe someone else can shed some light. I quite like the idea you've got there.