Rent eight full sections of scaffold, eight adjustable legs, a few small platform style planks that span the interior of the scaffold, and two of the widest, longest stages ( big aluminum planks, as in 20' or 24' x 2' wide) available. Erect two towers, span them with one stage to stand on, and one behind that, at hip level, to function as a workbench/safety rail. About as safe as it gets, comfortable, and very efficient.
Ladders, as you correctly note, suck, and pump jacks are a total PITA, and dangerous. Rent what you need from a professional scaffold supplier, do the job, and call then to pick it up. No big investment, and nothing to suck up all kinds of space for a job you only do every few years.
As for Greg's vinyl comment. I respect Greg, and I live in a region where vinyl dominates the market. It's cheap, durable, and will last at least 25-30 years with almost zero maintenance. It makes a lot of purist puke, but it's also pretty effective in getting the job done for a fraction of the cost of more desirable choices.
