"Go To Portal Row"
You would need to tie that script into a layout script trigger OnLayoutKeystroke that processes actions for your up and down arrows.
Have to love the OnLayoutKeystroke trigger. Would work great in a situation like this. May need to setup some sort of If Statement to specify when it actually progresses with the Go To Portal Row. Otherwise if you are in a field outside the portal it will still try to take you into your portal. May not be an issue for you and it should be pretty easy to workout.