Goodness Bonkers, I am so sorry to hear about Jasper.......
If your friend said his paw pads look a little dry, is there perhaps a crack where the pad comes into the toe? I have had experiences with dry, cracked pads on kitties. Often these cracks are leading towards the toes and sometimes tiny pieces of litter get stuck in them, causing pain and potential infection.
You Bonkers, would absolutely be able to see this if you can get Jasper nice and comfy snuggied in you lap.
The other thing could be a soft tissue injury to the paw itself. Soft tissue injuries do not necessarily produce swelling and if there is no swelling they generally will not show up on an x-ray. Soft tissue injuries are able to be felt/palpated and there is generally no treatment other than telling kitty to rest.
Vets are so silly.......the only way to "rest" a kitty is to glue him to the floor.........

Bonkers, do you have a heating pad that you can set on low for Jasper for him to rest his foot on?
I'm not a big fan of prednisone, but if absolutely necessary, a kitty should always be given
prednisilone as opposed to prednisone. Kitties do not have the enzyme to convert the prednisone to prednisilone, so only if necessary, the best is prednisilone.
Concerns about prednisone are that it suppresses the immune system.
If kitty is a diabetic, it can louse up the glucose levels.
Pred also really delays the healing process, both in humans and furkids
Thes are my issues with pred.
Sending prayers and positive healing energy for Jasper and his worried meowmie.