You can do this in several ways.
1.There is a bike trail that goes a little under 5,000 miles.
http://www.adventurecycling.org/routes/lewisandclark.cfm
2. Visit each of the states on the trail by car motorcycle etc. and do something fun there.
http://www.lewisandclarktrail.com/
Some more helpful links
http://www.lewisandclark.com/
http://www.lewisandclark200.org/
http://www.explorethelewisandclarktrail.com/
