A password protected zip file is just as suspicious to AVs as the original rom

In that case, how about using extremely trivial encryption (eg., XOR every byte with 0x3B) and on the website give a one-line perl command to decrypt. Now it's random data and not a known format (like a password-protected zip file).

Of course, any AV company could add a rule to their signature checking to undo the XOR if they were targeting the romhack.ing site, but it sounds like they aren't being targeted but just getting caught up in the dragnet.