Watch the D Lydian 2 online guitar lesson by Robbie Calvo from 50 Modal Licks You MUST Know
The opening phrase to lick 23 is built from a D major 7 arpeggio, which means I'm really outlining the underlying harmony for solid melodic structure.
The Diatonic Major and Minor double stop 6ths sound really sweet over this track, especially with a little overdrive and delay. You'll notice I repeat the first three double stops before ending the phrase. I like to play double stops by picking them with fingers and thumb rather than using a pick. I can control how much of each note in the double stop rings out by approaching it this way. Nothing wrong with using a pick, the choice is always yours.
Try creating some other double stop 6th ideas over the track and record them if you can to give yourself a critique always a valuable way to practice!