Rough finish to plaster

Happy new year all! I've got an odd question - how do I make my plastering look rubbish?
The client (bless him) would like me to match my plastering to what he's got in the rest of his very old house - the finish is rough and resembles artexed ceilings (but not as rough) i.e. almost like brush strokes.
I was thinking of using One-Coat to get a softer finish and then using either a sponge or a large paint brush to rough the surface up a bit.
Any suggestions?

textured roller

Just thought I'd let you know how I did it in the end - I used One-coat, got it to to stage of looking nice and flat and beautiful and then distroyed it by going over it with a sponge in a bag.

Ended up looking pretty good if I do say so myself - matched the old plastering spot on.