You could buy a board cover and this: https://www.amazon.com/dp/B07LGM869B/ref=cm_sw_r_cp_apa_glt_i_2RQ8RSDZ1XFZP7CC22AG

Also use another strap to keep it flush to your backpack. Wouldn't want to take a sudden turn and you whack a kid hard enough to send them to the orthodontist.

If you ask me though, I'd just use a carabiner and some sort of rope instead of the Amazon thing. Attach it to your bag handle or to the top of the straps.

I'm grabbing an ATLAS so I can't comment on wanting to really try that with my current backpacks... Wave seems like a great size, but I guess I didn't really think of that.

There's also this option: https://www.amazon.com/dp/B08TTDDL6Y/ref=cm_sw_r_cp_apa_glt_i_CHRX39YY57PB06RFH40A

And the carabiner and the strap for turns.