I assume you are talking about the figure shown in analog stats for your domain. If so, I don't think you can change the way it 'counts' distinct hosts, other than changing the stats package you use.
I use TraceWatch on some of my domains, it provides real-time stats, which I find extremely useful. It does however require a line of PHP to be added to any pages that are to be counted. It is also a bit tricky to get working under PHP5.
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