With 710 rc2, the lirc embedded transmit device attached to the mce usb receiver, just worked. I didn't have to enable anything special.
I have one on each of my MD's, and 1 has a dish receiver, and a 32" TV attached to it. I just plugged in a dual headed emitter to port 1 (AFAIK port 2 does not work) and learned the codes for both on the USB-UIRT in the living room. And after testing them, from the learning page, and doing a reload of the router, they work well.
Just recently I also added a Roku Netflix player to this same MD, directly atop the dish receiver, and it also gets controlled by the mce blaster.
If you have more than one (as I do) just make sure you are choosing the correct lirc-embedded-transmit device, otherwise you'll have IR signals bouncing all over the place
as I first discovered!
But in short, there is nothing special you have to do other than tell the device template which transmit you want to use. Re-Load Router and enjoy.
I have all of my dish tuners, and the roku box, available as "LiveTV" devices throughout the house. MythTV automatically chooses whichever dish receiver is not in use, and the control is seemless. So yes, I would give access to all MD's.