Ah, now I see. Unfortunately, I don't have a solution because I think the example is misleading. I suspect the parm in question was supposed to be a user-defined parm not an internal one. But that's pure conjecture on my part.
Anyway, the only other suggestion I've got is to use the internal "Load Generator Name" parm, instead. It's still not a "User id" (like the one assigned to/by web_set_user) but might give you something more meaningful than the LR-assigned VuserId.
The lr_whoami(); function will return what is described in help. If running in Vugen on your development system, the id will be -1.
When running the test, expose/expand the information about a specific Vuser. This will show the Vuser ID. That is what lr_whoami will return. You can use lr_message, lr_output_message, or lr_log_message to output the info you desire.