Beside the butterfly groin stretch, there is the wall assisted stretch.
(1) Lie on your back with your hips close to a wall. Extend your feet up the wall and spread your legs as far apart as possible. Gravity will assist the stretch. Relax the weight of your legs into the wall, keeping them straight. Hold a while, 3 breaths, then seem if you can move the legs a little farther apart.
Move away from the wall, if you feel your hamstrings though, but don't let your tailbone lift off the floor. If your knees strain, bend them and place your soles of your feet on the wall, knees point away from wall.
(2) From the same starting position against the wall, bend your knees and place your soles of your feet together, gently press your hands into your knees to open them out as far as possible. Don't let the tailbone come off the floor. This exercise is similar to the sitting position from the post above, it is just wall/gravity assisted. TW