Wow, interesting question.
So, you want to go steep and heavy, and 1:1 gearing 30tx32t doesn't give you enough power?
It depends on the cassette, but a lot I see have maybe the first 3-4 smallest cogs removable, while the large ones are fixed in place and not removable (not always the case, but that is typical). If you do go that way and make a 6 speed, one option to look at is the "single speed conversion kits" as they allow you to place your cog(s) anywhere on the cassette you want (outboard for you) - they have a ring that bolts onto the cassette to hold it in place.
As for derailer - you need one with a long cage (you can convert short cages to long fairly easy) if you want extra large cogs. To some degree, you can limit the movement of a derailer to (theoretically) only allow an 8 speed to reach 6 of the speeds. I'm not sure if there is enough adjustment to go as far as you want though. I've gone one, but never two.