Both bus bars will have to meet somewhere, that somewhere is your 0v reference, pick the last two caps in the power supply, join their -ve together and call that the 0v point. Take every other power supply cap -ve to that point apart from the first cap in each half of the power supply, take their -ve back to the -ve onto the bridge rectifier. Then take a single connection from the each first cap -ve (directly on the cap, (don't be tempted to use somewhere on the way to the bridge) to the 0v point.Using twin busbars, one running along each bank makes it virtually impossible to ground without introducing noise all over the place.
At least thats what I would do.