I had my port placed on the right as I am always the driver ( so shoulder belt over the left side )
as a passenger ( rarely ) I would pull the strap down to my upper right arm area so not directly over the port
AND may have even put it under my arm once
BUTT ... could always try some high density foam ( upholstery cushion type ) under the shoulder strap / over the port,
to cushion the direct pressure
BUTT ! ..... it would not prevent pain if you are in an accident and the restraint locks with forward body motion
(( ...AND I probably shouldn't tell y'all this ... BUTT .. most modern lap / shoulder belt systems have a "lock-out" option which is used for kids car seats.
basically you pull the belt out to its limit to disengage the free riding mechanism, and gently retract the shoulder belt back to the "snug" limit which secures the car seat in a solid position i.e. doesn't let it lurch forward until it locks ...... SO if you "snug" it so it is a bit loose over the shoulder it would still provide restraint ... BUTT not put direct pressure over the shoulder area.
NOT SAYING anyone could or should try this, just letting y'all know how shoulder / lap systems work.
AND if you are in an accident it will hurt like HELL
regardless of where the strap is.
REMEMBER once we had NO seat belts ... then they added shoulder restraints and then air bags ....