I do not know of a perl binding for the Aqua Tk toolkit (but that does not mean there isn't one).

If you wanted the start using the Aqua toolkit now with a minimum of fuss, just write the GUI in Ruby or Tcl, the rest of the program in Perl, and open a pipe between the two components to connect them. I don't know about Ruby, but Tcl is a very easy language to learn and it would take little additional time to build the GUI in it.

Having the GUI code separated from the main engine also has the advantage of allowing testing of the engine in a CLI environment, something that should appeal to vi-types.