I am so very sorry that your little one has to go thru this. I can hear how difficult of a decision this was for you to make in your post.
I have heard/read of others making a sling out of a scarf and holding the pup up to potty after a surgery.
I will keep our little one in my thoughts and prayers that he heals quickly. If you do not mind my asking, what brought you to this surgery? Hugs to you and your little one. Bo