If it is relatively fresh, I think you would be fine just pitching the whole packet. If it is towards the older end of the spectrum you could have two options to choose from -
1. A vitality starter - just spin it on the stir plate in a quart of wort for 4-6 hrs then pitch the whole thing.
2. Do a SNS (shaken-not-stirred) starter and pitch the whole thing at high krausen. But you need a proper shaped vessel for that to pull it off properly.
----if it were me and the packet was reasonably fresh, I would just pitch the packet (especially if the beer in question was not for a competition or I was not planning on reusing the yeast).