Not meaning to sound like an ahole, but your bike should already be comfortable. If you have made it look good by let's say removing the passenger pegs, you'll want to replace those as you will be wanting to shift your butt around. Passenger pegs afford that. A 1000 slab ride is not much different from a 600 mile secondary roads ride. They are both 'all day' in the saddle.
The Iron Butt Association has some tips
http://www.ironbutt.com/tech/aowprintout.cfm
