Make a .bin file out of it, AKA MacBinary. I recall there even is a module, Mac::Conversions, which can encode and decode the file for you — assuming you're trying process the file before upload through MacPerl. I can only assume that is what you're trying to do. If not, perhaps the module Mac::Macbinary could help, it allegedly works on non-Mac platforms too, though I have no experience with it whatsoever.

A MacBinary file is a flattened file, with data fork and resource fork both stored in a normal, non-Mac compatible binary file, and with the original file name, creator type and file type somewhere in there as well. If you append the ".bin" file extension, a Mac will most likely recognize it automatically.

Another possibility is a .hqx file, AKA "BinHex", but that will make the files 33% larger, and smartass browsers on non-Mac platforms may try to decode it for you, if somebody is trying to use such a browser to download the file.