I'm pretty sure this works on at least 9.3.0+ and probably earlier code. You have to have a member of the pool otherwise it will not config sync as you found out. I recommend using an IP that does not exist. I'm guessing that you have a Default Node Monitor defined (under Local Traffic -> Nodes) and that is causing the problem. After you define the random node in the pool that doesn't exist, find that node listed under Local Traffic -> Nodes and specify that there should not be any node monitor for it.
Hope that helps!