u can try the fuel and load planning tab in fs. the aircraft view from the top down with the crosshair will tell you the CG. count the bars from the top (there are 33 in all) and see where the crosshair is then calculate the percentage and u should have it fairly accurate i think.

eg* 16(the bar where the crosshair is) * 100 / 33(total # of bars)=48.48..
this is the cg u will use in flight and to set the stab trim
in addition u will also need the ZFW and all the goodies which can b found here.
happy flying :)