Hi Dan
thanks for your help. I think I spotted the errors. First I was not using the right RegEx.
I realized just now that the full path on which a custom request gets returned is given by the sServiceUrl on which the mock server is "listening", concatenated to the RegEx.
On top of that, the simulate method was invoked after adding custom requests to the mock server, actually overwriting those.
After this was configured, it worked 
Thanks, regards
Vincenzo