Hey Ringo, I'm a fellow Huon-villain as well
Mt Picton is awesome - great scrambling up on the summit ridge and some interesting rock formations and alpine tarns over on the NE side.
Adamson's Peak is a long day walk, but the forest is beautiful and the views are incredible. Not too much in the way of big rocks from memory, but certainly a large boulderfield around the summit.
Same with Snowy South/Lake Skinner (probably my favourite walk in the area). Stunning forest, great variation of terrain/vegetation as you gain altitude, crystal clear alpine lake and awesome view from the summit (assuming a clear day:). Very few bouldering options, but tonnes of rock-hopping in the open country on the ridge.
One to consider would be Cathedral Rock. Not as long (unless you can organise 2 cars and turn it into a Montague Thumbs/Mt Montague/Thark Ridge/Big Bend traverse), but really impressive taster of the Tassie outdoors, capped off with a short scramble to a truly precipitous summit tower (200m drops on 3 sides) with a really interesting outlook on Mt Wellington from the south.
North West Bay river makes up part of the track, and if you are lucky you may even spot a platypus or two
If you are doing the traverse on that one (or Collins Bonnet) and happen to find yourself over in the Big Bend area, your mate would love a look at The Lost World for sure. Plenty of rocks over there!
One more thing - assuming your mate is from the mainland - make sure he brings Tas-appropriate clothing. September can still be pretty nasty - especially in the mountains. Sounds like you have some experience in these things, but, as an ex-mainlander myself, it's worth mentioning. The differences were quite a learning curve for me, that's for sure...
Have fun!