Currently the IR Blasters/Transmitters that come standard with the PVR150 PVR250 and PVR-USB2 are not compatible with LinuxMCE. You can use them to control the cable box with linux, with LIRC. I have been using them to control the cable box with mythtv for a while, but as to integration into LinuxMCE there is none. I am not a programmer, so I can not point to any direction to begin. I would imagine that adding this blaster transmitter would be a huge help to expanding LinuxMCE. This blaster come with most of the cards we use, but unfortunately the only blasters supported are ones that require an additional expense.
There were a couple other post refer to others who were considering starting the coding, but I have not heard anything active.