[tz] TZ from lat/lon?

Hello all, Not sure if this is the best place to ask this (and if not, I would be very thankful for any suggestions), but does anyone know of a decent open source lat/lon-to-timezone package that runs _standalone_ (as opposed to querying a server somewhere)? I am aware of a few networked solutions (e.g. earthtools) and at least one commercial package (askgeo). The former won't work standalone, while the site license for the latter is too steep for my noncommercial, one-off project. Thanks very much in advance, HJ