Yes, if your TT bike uses bar end shifters but you'll have to run them in non-indexed friction shifting mode and you'll still want to double check the derailleur stops to make sure you don't shift off into the spokes on the low gear end or into the dropout on the high gear side. But if you run STI style brifters on your TT bike or want to run in full indexed shifting mode then you won't get clean shifts if you try to run a 9 speed cassette on a 10 speed system.
-Dave