I've been to a few cons and I've even covered costume parades for a certain comics news site, but I do not ever recall seeing any Doom Patrollers. Seems to me Negative Man wouldn't be too bad a choice for a con costume.
Shag has shared the love with a plethora of other websites, some of which are listed right here:
Aquaman @ The Aquaman Shrine
The Atom @ Power of the Atom
Booster Gold @ Boosterrific
DC Cosplay Obscura @ DC Bloodlines
Doctor Fate @ Tower of Fate
Firestorm @ Firestorm Fan
Flash @ Speed Force
Hawkman/Hawkgirl @ Being Carter Hall
Martian Manhunter @ The Idol-Head of Diabolu
The Vixen and Zatanna @ Justice League Detroit
Wonder Woman @ Diana Prince is the New Wonder Woman
Check out those other sites and come on back to MGA80 soon.