I'm afraid you're out of luck.

The value of a tied hash in a scalar context is currently undefined. When 5.8.1 eventually rolls around you'll get a fatal error if you try. See this perl5-porters summary for more details.

Yet more discussion can be found in the perl5-porters mailing archive here, here and here.

As sauoq correctly pointed out overload shouldn't work since it applies to the underlying object used to implement the tied hash.

The addition of an extra hash method to the tie API this was discussed, and might appear later (at least that's my interpretation of the bug's history.)