Add A Column To Large, Busy Table.

I have a table that currently holds about 5 million records. We add an average of 5,000 new records per day, all of them from overnight batch jobs. I guess it's not that big, but there are two text columns that hold a couple KB each, so the total size isn't exactly small either. The data is created from medical billing data we receive overnight. We get two reports- patient demographic information and a physician's dictation relating to that patient. This data is always one to one, and the purpose of this table is to store the data as we originally receive, which is why both reports are in the same table. After we extract the details from the report, (which are by this point always reduced to text documents) we need to keep not only the data but the original documents, hence the two text columns. We considered moving the large columns to their own table, which would just have an ID field and the column, but the powers that be really wanted all this in the same table. Nothing new goes into the table during day- it's all SELECT statements.

I need to add a column to this table. It's just a small char(7) column, NULLS allowed, of course. We bill for several clients, and reports from different clients become available at different times, so there's really no down time overnight. Altering the table during the day is out of the question. So how can I add a column while the table is active?

My best idea so far is to use SELECT *, NULL AS NewColumn INTO NewTable to create a copy of the table (using a cast to get the correct datatype) during the day, when no new data is going in, and replacing the old table with the new by simply changing the names right after everyone goes home. But this could still cause slowdowns while it builds the copy, and leave the problem of re-creating indexes (there are several). There ought to be some graceful way to tell it to add the column to the existing table and play nice with ongoing traffic.