simulated annealing package help

Hey all,
I was wondering if any of you guys know how to implement a penalty  
function with the gsl simulated annealing package.
I mean the following:
I am trying to minimize a certain function $f$ over a set $S$:
$$ \min_{S} f$$
using simulated annealing.
I know that SA will give convergence if I minimize the following
$$ \min (f+\alpha I_S)$$ where $I$ is the indicator function of $f$,  
with $\alpha \to \infty$.
So basically I need to add to the function of type "gsl_siman_step_t"  
an additional parameter alpha that will increase at each SA step. Any  
tricks? Any Ideas on how I could do it without changing the siman.c  
functions?
Oh anyway. Why did you guys try to be do polymorphic programming with C?
Many thanks and regards,
Fra