I am in the same position as need to take a suit to a wedding in Italy next week.

I am going to take the suit carrier (i.e free plastic cover that came with the thing...not a bought suit carrier) as well as my hand luggage sized suitcase and try and place it on top of luggage in the overhead bin. While it is clearly oversized as a second piece of luggage, I really think that common sense will prevail and unless the flight is packed, there will be no problem.

If challenged, I will simply put the jacket on and fold the trousers up to put in the suitcase...

It's a bit harder for the bride (on the same flight) who with the recent hand luggage enforcement is really worried that BA might make her check in her wedding dress. Again...I hope common sense prevails.