How pass a variable to provisioning module

Hi
How can I pass a variable to a custom function in a provisioning module from client area (productdetails).
Example:
Assume a client page with a dropdown menu that you can choose OS Template for a VPS from it, when you click "Rebuild" button; module calls rebuild function with "OS template" argument.
The question is how can I pass "OS Template" to "Rebuild" function?
Thanks