I fixed par2 so it supports UNC paths ages ago I just forgot to post it. You can get it here: http://dev.ismell.org/par2cmdline-0.4-t ... 03-UNC.zip
I have included the patch and both x86 and x64 versions. These were built using the TBB version of par2.
I hope there is interest in integrating the fixed versions. Then we can finally make the temporary download folder a UNC path