Equally, at most other ATC units, we will welcome you practising the procedure.
Most importantly, listen out on the frequency for at least 3 - 5 mins to ensure that the ATCO isn't too busy or about to commit themself to a time consuming procedure such as an SRA or similar.
Make it absolutely clear that it is a practice, try and make the scenario realistic (there's no need to scream
) and take part to the fullest extent possible.
At some units its just not going to be practical most of the time, but when it is, it's very good practice for us, just as it is for you.