Well, if you’ve run out of other options, you’ll have to enter the names yourself. You can do this either on an individual shot or a group of shots (you’d probably want to do the latter) in the Media Pool by selecting the shots, right clicking, and selecting “set reel number”. This will give you the same options as the configuration page, and you can then select “enter manually” and type in what those files need to have.
The path name parser is not a general expression parser and does not take general expressions as patterns. It is specifically designed to extract names from right to left, and those names can only be truncated, not concatenated.