I had SQ agents check me through to my final destination with a separate star alliance ticket two weeks ago. I was at SIN and the Star/KF Gold desk guy seemed a bit iffy at wanting to do it so I had to say please and thank you :-) Other lady seemed concerned about baggage allowance on other airline. I had a printout showing my baggage allowance too. A little more trouble that I would have liked but still they did it without a fuss. I've also done it with other Star Alliance airlines as well. Seems to work out usually.