Thanks for using JustAnswer.com, I'm Dr. Dan and I'll try to help you.
I'm sorry that you are having to deal with this.
When dogs swallow sharp objects we follow what the human doctors do to children. Feed your dog some food or treats with cotton balls in them, (not synthetic cotton balls). The theory is that the cotton will catch an protect the blade during passage. I know it sounds silly but there are many reports of the cotton balls and blades passing through without problems.
I hope this helps, best wishes.
As many as you can get him to eat, I'd try for 5-10.
Is there any chance the cotton balls could cause a blockage? How long till he might pass this?
If the cotton balls are synthetic then yes it is possible to cause a blockage. If they are real, then it is unlikely.
They will take 12-48 hours to pass.