I say go for it. The base Brompton frame/fork/wheels is probably as aerodynamic as most of the 700c wheeled bikes you'll be riding against. The most important improvements over a stock Brompton:
1) Aero position. Ideally use aerobars with bar end shifters. Profile ZBS TT aerobars would probably pack the flatest on the Brompton straight bars. It's really, really important that you're comfortable in your aero position. This might require swapping the stem for one with much more reach.
2) Gearing. You'll need high enough gears to be competitive. I'd pick their 6-speed configuration for sure. I think you'll want to switch to a larger chainring for races.
3) Tires. Fastest tires that fit the bike... Maybe Schwalbe Marathon Racer or Primo Comet