It might be more difficult than I thought. I found this in http://archive.develooper.com/perl6-internals@perl.org/msg11133.html

In perl5, one could only tie a hash..not a hash of arrays of hashes as a single object. To do this, you needed to have your tied hash return special tied arrays, etc. This is rather complex code to write, and rather slow, due to the generation and destructuin of all sorts of temporary objects. Damian's Regex::Common did this, but I don't know of any others. ... more