[boost] [Boost.Units] non-integral unit exponents

Hi, I'd like to use Boost.Units but am unsure whether I can declare a unit like this: W/m^2 Pa^0.25 K^1.523 In addition, I'd like the ability to change the pressure (Pa) and temperature (K) coefficients at runtime (user supplied input might change the default coefficients). Are these things possible with Boost.Units and, if so, could someone point me to an example? (I need this for nucleate boiling curves). Thanks. -- Noel