External Tools and multiple $FilePath$'s

I have created and External Tool action that successfully runs a command at the command line for a file using $FilePath$ in the Parameters. My External Tool menu item is active whether I have one or many files selected in the project tree, for example, but I don't get the list of $FilePath$'s correctly when attempting to run it on multiply selected files. Is there a way for me to change my External Tool action to get and act on a list $FilePath$'s rather than just one?

Regards,
-Vard Lott