Yes, there is! Make sure the Zune is closed and simply change the
genre property of the podcast/audiobook file to
Podcast in any ID3-tag editing software (the screenshot below is captured in the foobar2000):
The main advantage of the
foobar2000 is that it lets you modify a bunch of files at once. For example, if you click a right button anywhere in the
Properties window, you can select
Auto track number and it will put track numbers by the order they are located in the playlist (and sum it for you).
Zune has the tag-editing functionality too, but, apparently, changing the
genre doesn't make it rebuild it's cache and recognize the file as a podcast.
I've looked into this and currently it seems to be impossible to upload/manage podcasts manually (might change in the future, if someone will find a way to read/modify mysterious SER files). Tried myself, nothing works, both genre and file structure are ignored.
Source 1 / Source 2
Tried accessing the device over plain MTP (as it was suggested in the first source), but after a day of troubleshooting, driver modification, compilation of several libraries and experiments I found out that my phone got two comm endpoints instead of three (required by the standard). My hope died at this point.