cut off form factors

Hi,

I am studying the production of mesons in nucleon nucleon collisions at
energies of few GeVs using an extended linear sigma model. The effective
Lagrangian contains only hadronic degrees of freedom.

I have been using calcHEP for calculating the cross section and
already got good results with it. However, since I get an overestimation
of the cross section when the energy gets high, I need to include vertex
form factors which are a function of the particle momenta at each vertex.
What I need is probably an exponential function of the form
"exp(-f(p_1,p_2,p_3)/Lambda)" where Lambda is some scale. Unfortunately,
this possibility is not available in calcHEP. Now I want to switch to
MadGraph, but I can't really find out, if the implementation of such form
factors at each vertex is possible.

Could you please confirm or disconfirm the ability of MadGraph to include
such functions at the vertices?

Thanks for help
Khaled