applying forces in a Forcite dynamics run

hello all

let's say I want to add some force (e.g., costant force in the X direction applied just to some atoms) during a trajectory. I have tried to use something similar to the script posted by Reinier Akkermans (here), changing "Velocity => ..." to "Force => ...", but it does not work (it is like I had set nothing). How can I get this done? Shall I have to run the trajectory step by step using restart? Maybe by modifying directly atoms coordinates at each step? Is there any smart way to do this?

Thank you very much for the attention

Giulio