Well since for pretty much any 5 gallon batch of beer above 1.020 in Mr Malty a starter is a great idea, when I do a 2.5 gallon or smaller batch of beer, I don't bother with making a starter and pitch the whole tube or smack pack in.
The overpitching discussion is a debate that never truly will ever be resolved. There's as many opinions on that as there are brewers. Personally I think it takes a lot of yeast to truly reach the amount where 'overpitching" is detrimental to a beer. And I tend to side with those who believe that it's better to have too much yeast than not enough.
So to me doubling the amount for a small batch isn't really an issue. It easier than trying to not ruin the other half of the tube/smack pack. I just pitch it, and then harvest the yeast later.
If it's dry though, I have no qualms about just pitching half a pack. I then fold the packet over and tape it shut and store it in the fridge. Then either I'll pitch it for another small batch, or I will add it to a boil as yeast energizer.