Parking Brake

[ONETAL]

The dropper seat post lever didn't work, there's no friction on the lever. So I've used a Sram aero 500 lever instead.

[Audax67]

For a no-fettle solution, Velcro trouser tapes work well.

[skeltrike]

probably been said already, you can buy a simple brake lever with a sprung catch to hold the brake. I had a 'ancy hydraulic one on my old kettweisel but you can buy a simple one from mission cycles. you can also get a dual function one operate front and rear simultaneously.