Hi Jon,
Sorry you're having trouble with the push. I'd rather not do manual tweaks like this, bug instead fix the problem at the source.
Also I hate to tempt you over to the dark side, but would you mind trying push on darcsden? If it doesn't work there either, it might be a darcs issue. If it works there, clearly it's problem on patch-tag.
With regards to the tar file, I think there is a way to attach files in gitit if you use wiki mode. But really darcs (or any vcs) isn't the ideal way to be hosting large binary files. The right thing is to add some "non versioned" space on patch-tag where you can just push via scp. But I don't have that now.
Also sorry for the slow reply. Your plaint slipped through the cracks.