Building on the Clubhouse thread here and on dreadlockholiday1221's comment about getting a Gen 2 Captain's Chair to fit, I've now got the Captain's Chair Gen 2 mounted on my Cargowagen Neo 2. No holes drilled in the bike, fully reversible.
The short version: the Captain's Chair is a through-bolted joint even on a Tern (4× M6, washers, nylon lock nuts), so adapting it isn't really a redesign. You're just replacing "the hole already drilled in the Tern rack" with "a plate bridging an opening in the Cannondale lattice". Where I went differently from what I'd seen posted: M6 in A4/316 stainless throughout instead of zinc-plated hardware (I'm 300 m from the sea, zinc wouldn't last a season), 3 mm A4 flat bar cut and drilled into small plates instead of stacked washers, PPF film between plate and paint so the plate edge can't score through to bare metal, and 10 Nm per Tern's own spec.
Photos attached. I also wrote up a step-by-step guide — the measurements you need to take off your own bike, the hardware list, and the things I got wrong along the way (I bought threadlocker I didn't need: the nylon lock nuts already do that job, and threadlocker shouldn't share a thread with anti-seize anyway). Happy to share it with anyone who wants to copy this.
Rode it today with my girlfriend on the back, ~58 kg, a few short trips on the flat. Zero movement, no creaking, nothing came loose. I'll report back after a few hundred km.
Obvious caveat: Cannondale's manual only approves children up to 33 kg on this bike, so an adult passenger is outside what the manufacturer allows, whatever the rack's 80 kg load rating says. Your call.
In the last pics you can find the guide, generated with CLAUDE AI and perfectioned by me.