While the rules may vary for the Department of Commerce,  for the DoD this would definitely not be legal.  Numerous fiscal lawyers have discussed how you cannot use any means to extend the life of a multiyear appropriation past it's Congressionally designated timeframe (as this questioner is suggesting).  This scenario in DoD mostly comes up with organizations that want to use the 2410 Severable Services exception (which only applies to annual appropriations) for multiyear appropriations (which you cannot legally do). 

In DoD, multiyear contracts are a contracting exception (not a financial one) and they are funded just as you would any other regular contract - on an annual basis.  Multiyear contracts also do not exempt you from the Bona Fide Needs rule.  Therefore, in DoD, this question would not be legal on a few counts. I recommend speaking to your legal, since the Department of Commerce  might possibly have different regulations.