Emulating this is a bit hard, since mRatio doesn't download any files and thus doesn't let you pick individual ones.
Open the .torrent file in BEncode Editor. Find and add the size in bytes of all the files you want to look like you're seeding. If the result is not divisible by 16384, round it up to the next multiple. Copy the final number, then use the same program to open the torrent's settings file under "mRatioTorrents" (mR must be closed beforehand), find the fake left value, replace it and save.
See here for a way to find client file passwords.