Yes, I've run into this and solved it this way...
Create a ~/.ssh/config file for your personal custom config, and add
This says - for these hosts don't prompt for keys and put them in a special file so they don't clog up my "real" host keys. If you add them to the normal file it soon becomes a mish-mash of irrelevant keys. The identity line makes it so you don't have to keep typing it manually for these hosts (use the right filename of course).
You'll see the host key fingerprint message still but no prompt or wait.
Actually this file is great for specifying non-standard ports for certain hosts too - then you don't have to keep putting -p 7777 to login.
I've got the "Custom AMI Shrink Tutorial" done. Just testing a bit before posting.