I've been racking my brain trying to come up with a reason why it wouldn't work, and haven't been to think of anything. So unless someone else can figure out why not, I think you should be good to go. Its not like the higher pressure will move the beer through the cold plate any differently.
The only thing I've been able to come up with would be that storing the beer warmer would result in some CO2 coming out of solution and you'd have to turn the beer gas up higher to compensate than you would plain CO2. But since its a stout and you'll be knocking a lot of that CO2 out of solution anyways, not to mention serving it all within a day, I can't see that being a problem. Good luck at the competition!