I know of one or two addons back around patch 1.7 or 1.8 that could do this. But then they changed what Functions could be used by addons. I haven't looked at the code for XPERL, but I don't think it would be that hard to use the already existing xp bar that shows up for your character and modifying it so it could be shown on the party character windows. Broadcasting between the clients should be the easy part.