Assuming you don't want to modify the pump itself, and the baffles are not doing everything you want (pick-up still gets air on hard deceleration), you can just squash an O-ring in between the tube and the fitting on the cover, then attach a strap from a pump cover bolt to the head to prevent it from swinging and eating the O-ring. Just large enough to stop free movement is probably enough, doesn't have to be a press fit. If I had to, I'd use a piece cut from a bicycle tube!
I would guess that the cotter pin operates in a slot long enough to permit the tube to swivel, but not come out? If you can close up the slot (weld) you control where the pick-up can get to.
Is there enough pan depth to lower the pick-up by splicing in more tube between the swivel and the head?
