Best practice here is to have Hardware Conferencing resources available at your branch office.  Do you have any spare DSP's available in your Branch office Voice Gateway?  If not, do the IP Phones at the Branch office have access to the Conference and Xcoder resources at the HQ site?  If not, add them to the Branch office Media Resource Group.  You could also use the software resources from your callmanager.  Create a new MRG called Software_MRG, add the CUCM Conference and Xcoder resources and this this MRG to the Branch MRGL.

HTH