LMCE's version of MythTV still runs a mythbackend server. As long as your versions are close or exact, you should simply have to put the MythTV frontend PC on the same subnet as the core media subnet (default is 192.168.80.1) when running mythfrontend it will ask you for the masterserver backend ip address or hostname (again the default is 192.168.80.1 or dcerouter), after providing this information, you will most likely be able to connect to your content (I do this all the time from my laptop booted to kubuntu 710, and the mythv-frontend package installed) and I can view my recordings and watch TV live from the tuners.
the latest version of MythTV in LMCE is 0.20.2 fixes, so as long as the version you install is of this variant or package level, you should be able to connect up. If you for whatever reason do not wish to attach the myth frontend pc/laptop to the media subnet provided by the core, you will have to make ammendments to your LMCE firewall from the web admin to allow mythtv to talk to it, or simply disable the LMCE firewall so that the mythfrontend can connect to its address. You will also have to go into mythtv setup on the lmce core, and get the username and password for the mythtv mysql user. Otherwise you will not be able to connect to the LMCE master backend.
Hope this helps.