About 97% of each torrent is the PIGG data, which is the same for both. So if you have the PC version and want to help seed the Mac version:
- Start the torrent and let it create the directory structure
- Stop the torrent
- Copy the contents of "CohBeta\piggs" to "City of Heroes Beta Mac.app\Contents\Resources\transgaming\c_drive\coh\piggs"
- Force the torrent to re-check
- Start the torrent