I primarily use my 17ft Prospector solo, I know it's not ideal but it works surprisingly well for me and my large dog(s). 
I obviously paddle the boat 'backwards' when I'm solo, and as I result I find myself leaning on the second thwart that's directly behind the bow seat. They only add this extra thwart on the 17ft model for extra stability I believe. After a long day on the water this can generate a fair amount of pain in the backside. I plan to buy a kneeling thwart in the near future to replace it with, but I'm wondering if I could get away without having this thwart installed in the meantime? The seat is bolted to the aluminum gunnels (on a drop bracket) so I'm thinking that would add enough strength? Keep in mind I am very easy on the boat.
Thanks!