Custom Commands: Cannot Use !* as Prompt Defaults

I'm running into some issues with the prompt feature of custom commands. I need to be able to set the filename as the default for a prompt, but no matter what I do, I can't do it. Escaping with \! (for filename) or \!/ (for directory) reads the default as '\' and quotes did the same thing so I'm stuck. Any suggestions?

cp ! !?directory:?"!/"!!?filename:?"!"!

Also I'd like to be able to get the filename and extension separate, so I can just append something to the end of the filename, but before the extension.

Usually I like to append a date/time to the end, so maybe some date/time functionality would be quite useful as well.

This is not possible unfortunately.

Also I'm not going to turn the custom command functionality into scripting language :-)