Depends which DLC. if you mean the weapon ones like the gold ones there are already servers that have the weapons modded into the game (for free) The player models you could probably just make a replacer for (replace one of the crappy models you get for the steampunk ones) otherwise considering it's by tripwire i don't think you could bypass the online DLC check. unless you just pirated the entire game but then you wouldn't be able to whore them online.