Delay one channel (left or right) by 20 ms
Do you actually do this? Is there software that can delay the audio output of your sound card by channel?
Even if so, I don't have many mono tracks and it'd be at best a curiosity, and sadly not a substitute for what I want
Well. It's actually something I do on FL Studio, with a VST. There are many freeware VSTs that can do such thing.
As for actually delaying one channel in your sound card. I have no idea. You could probably find a plugin for Winamp that does such thing. I think i have used this decoder in the past http://www.winamp.com/plugin/winampac3/221648 It says you can set up a delay per channel.
But yeah, it is a curiosity :D It doesn't sounds great for everything. I mean, you can't delay one channel of a song and expect it to sound good. It's used sparingly on a per-track basis when mixing audio, often with further processing so the sound doesn't filters itself out when played on speakers.