I came up with a fundamentally "agile" solution: break the problems down into smaller tasks until the first task is too small to offer resistance.
E.g. rather than "write architecture specification", start with "outline the heads for architecture spec" and then maybe "draw rough sketch of architecture on paper" and then maybe "write introduction".
Almost everything in my to do list these days can be executed in under 10 minutes. As a bonus, it gives you the dopamine hit / satisfaction of watching a stead stream of items moving from 'todo' to 'done' state on a daily basis.