Hi John,
I dont believe this can be done out of the box using an event/trigger, as the spel code behind it to do that functionality doesnt exist out of the box. For something like this, you may be able to do it using a data partition constraint on CIs as a "create" - such that the name cannot already exist. I am not sure of the exact syntax off hand to be used, but if you look at existing constraints you may be able to piece it together that way and test it out.
The only other way to accomplish this would be using custom spelcode, which can certainly be done, but is outside the scope of support. You may get some info here on the communities from folks who have done something similar if they are willing to share it.
Hope this helps,
Thanks,
Jon I.