mod-security replace characters in POST body

Question

I want to replace all the non-alphanumerical characters in the request body (not in the parameters themselves, but their values) with nothing using mod-security. For example:

# Initial request
param-1=val@@#ue1&param-2=value{^%2 

# Changed request
param-1=value1&param-2=value2 

Tried this method including some other common ways I found, but none of them seems to be the way to get this to work.