My apologies for not getting back with you sooner. Life's been really
hectic and my inbox was the first casualty of it :).
That being said, we did a bit of work on the upload UI to move it to a
shared location so all themes could use it. As part of that I actually
removed the "CUSTOM" option but I'd like to add it back in. Just a heads up
if you update and notice it's not there.
We're using plupload for the uploading. The POST params are set inside the
JS code which can be found here,
The form parameters need to be explicitly included here in the JS for the
server to receive them with each photo post.