Watch the Adding the Major 3rd online guitar lesson by Fareed Haque from Jazz Rock Workshop
One of the coolest things about jazz and blues is the way western European harmonies and African pentatonic modal scales have had to adapt and accept each other (if only we could all do the same). Pentatonic scales have integrated many of the key notes and concepts from western diatonic harmony (especially the concepts on I, IV and V chords and the notes that come from those chords). Western harmony has had to integrate what were originally notes outside the western 12 note scale. The blues note was a result of this western approximation on the original ¼ tone pitches that African and Arabic cultures use to this day.
You will notice that the Major third will imply the Major I chord, while the Major 7th (the third of the V chord) implies the V chord. The Major 6th, the 3rd of the IV chord, implies the IV chord.
So the pentatonic scale has integrated into it the basic notes that give us the I, IV, and V harmonies even while we sit on a one chord vamp. What we end up doing in many cases - and this is very important to understand - is creating a chord progression on top of a one-chord vamp.
Just so long as the chord progression you imply eventually resolves back to home, it'll create drama, tension and hopefully a nice shape to your solo. Don't forget to add these notes in all positions.