Thanks for all the feedback guys.
I've been experimenting with my seating position on the last few rides and reckon I've worked out what changes I need to the seat. I think the Corbin seat is not what I need. I also checked out what the seat mod would be like with the front lifted. I don't reckon that will do it either.
Yesterday I rode an hour and a half to work (I work on different sites all over the place). I happened to have my work shorts on under my riding pants. This provided some surprising cushioning, especially when I pushed myself back a few inches so my tailbone was up on the edge of the pillion seat.
Everything just fell into place! It tilted me slightly forward, the forward controls were just far enough away, my weight was balanced between my backside, and my feet - it was like riding a different bike.
The trip involves about an hour on the highway at 100kmh (62mph). Normally after that trip my arms and hands are tired from hanging on, against the wind in my chest, and my legs are tired from the effort of keeping my feet planted on the pegs (I think that's a weight distribution thing). This time, it was just comfortable all the way, and no fatigue. Although, it was odd sitting perched back on the edge of the pillion seat, but so good it was worth it.
So the solution is just to be able to move a bit further back. I also like being able to move back and forward on the seat to change the position of my legs - further forward for intersections and around traffic, and further back for cruising on the highway.
So, I reckon I need to cut the pillion seat down by about an inch, raise the drivers seat foam as high as is practical, and smooth out the curve between them. That should do it. Very similar to a couple of mods that have been posted in this thread - so I know it can be done
Thanks again guys.