Unfortunately, they do not make periscopes for bass drums. I can think of a few solutions.

1 - Put them on a smaller drum. I know they've trained for that part of the multi-person instrument, but a smaller drum will allow them to see over.

2 - If the problem is on the marching field during show run, more reps and make folks around them aware that the drum will not stop for them if they're in the way because they can't see. (This should always be true anyway.) When it's not time for drill, have them remove the harness to one shoulder. This will allow them to carry the drum and see around. (This is how I carry them when moving place to place.) When learning drill, do away with the instrument and go with just the carrier until they're confident in the steps. Use peripheral vision to keep up with ranks around them in parade marching.

3 - When not on the marching field, have a friend escort them. Doesn't have to be the same person every time, but I'd recommend an upper classman who can "adopt" this student and help boost their confidence.

A LOT of us out there have had more than a fair share of bruises falling over something and onto the drum because of the nature of this beast. It's probably going to happen. Some things in life are like that. Best of luck! I look forward to hearing other suggestions!