i do my borders last when quilting on my frame.
when i reach the bottom of the quilt i do the entire bottom border.
then i do the left side of the quilt border then i do the entire top border.
finally i come down the right side border to finish up the borders.
if you are going to be doing your borders with a panto or with sew boards you would have to reload the quilt to do the left and right side borders but this really wouldn't be that difficult.
most LA use a quick loading type of system with leaders and either velcro or zippers and it would take about 10-15 minutes to unload and load the quilt to do each side.
i've always preferred to work from the front of my frame with freehand and ruler work.