You don't need any special coding, just wait until one loads through the updater before trying to start the second instance.
It's helpful to use windowed mode, and personally, I use the " -fullscreen 0 -maxinactivefps 5 -maxfps 20 " flags when I'm running multiples.
And to be clear, to run multiple instances, you need multiple accounts. Can't login the same account more than once at the same time, unless you're loading one copy of Test, and one of Live.
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I play on a Dell Inspiron 1520 laptop, and when my second account is active I can log into them both simultaneously. That's with the graphics settings turned way down admittedly, and I only use it to invite my alts to my personal SGs, but I daresay a more powerful machine could run two accounts at a decent performance.
You can run as many instances as you have accounts, and your compy can handle. I know one person who has run 5 accounts at one time, on the same computer.
Now THAT is the compy for me! 
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I forgot to mention that if you're going to be running a lot of intensive stuff, it's not a bad idea to run each instance in safe mode. Just remember not to click on options as it'll save your current (crappy) graphics settings. I can get 3 - 4 instances up like this depending on what I'm doing.
To give a point of reference: I have an E6600 Core2 Duo, 2GB of RAM (WinXP) and a 7950GT graphics card. I often run two instances side by side in windowed mode on a widescreen monitor. I have AA and AF turned on, bloom turned off (it's ugly), world detail around 110% and character detail around 150%.
I would not want to try this in any raid or mass combat situation, but I can run missions this way with no problem.
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I think what you are looking for is the bypass for the updater.
If you don't want to wait for one to fully load first, you can load the instances simultaneously with this shortcut:
"C:\Program Files\City of Heroes\CityOfHeroes.exe" -project coh
SunGryphon mentioned it as part of command line switches, but it bears mentioning separately: the /maxinactivefps command is a lifesaver when running multiple instances. I use /maxinactivefps 3 but use any low number that's not 0 to make your machine work a lot less.
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Greetings all...
Before I get burned at the stake, yes I did search for this topic...because I know it's buried in here somewhere. I think I might be using the wrong search words.
I'm looking for the coding that allows for a single computer to run an additional instance of CoH.
Thanks in advance for the assistance...it's much appreciated.
~ Jonathan