From a glance at the code, it seems a handy module when doing REST with CGI.pm-like modules. Good that you released it and the insight it provides along with it to the puplic!

What remains is the handling of large uploads by handle only. Admittedly, I handled it a bit heavy handed in my patching of CGI::Simple. Still, I see no alternative to switching between handling smaller requests by slurping it all into a var, while larger requests need to remain on STDIN and be read() buffered. Can be done by wrapping your get_body() method with an if/else switch based on POST_MAX.
Or could be that the abstractions that modules like CGI.pm provide are by design opposites of the low-level access my specific scripts require...