Instruct participant to lie on floor or mat with legs bent. Stand near their feet facing them. Assist them crossing their thighs, placing outside of one knee close to top of their other knee. Bend over participant's hips, position their foot of closest bent leg on your chest or shoulder while grasping their lower leg, in addition to knee of opposite leg with other hand.
Push your bodyweight down on foot while pushing down on side of participant's knee. Hold stretch. Repeat with legs in opposite position.
Low back may be stretched if hips raise off of floor significantly. If spinal flexion is not desired, care should be given to keep back of hips on floor by monitoring hips position and pushing downward instead of toward participant's chest. See PNF stretch techniques. Also see Lying Piriformis Stretch for similar static stretch.
Other (see comments)