I'm not sure why you'd need to try to thread this. Assuming you're doing this with a Bulk Insert process, BCP or a CLR SQLBulkCopy object, 100K rows should be inserted in the blink of an eye (unless the rows themselves are HUGE, which would slow down any process you set up).
Try taking a look at the SQLBulkCopy object. One way or another - it should be your friend. If you find that the 100,000 makes it too slow - consider setting the timeout lower and/or the batch size to a smaller increment.
http://msdn.microsoft.com/en-us/library/7ek5da1a(VS.80).aspx
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Your lack of planning does not constitute an emergency on my part...unless you're my manager...or a director and above...or a really loud-spoken end-user..All right - what was my emergency again?