Felix hey Felix, have you tried a similar stretch sitting down? Sit on the floor back straight, legs out in front of you. Open your legs as wide as you comfortably can until you feel a slight pull on your thighs, hands on knees or on the floor in front of you to steady yourself as you lean forward, with straight back, as far as you can then straighten back up again. Do it several times as part of your routine. After only a few sessions you should be able to touch your forehead to the floor. It's good for inner thigh muscles and helps keep you supple. Very quickly it becomes easy so mind you don't bang your head like I did!
You could turn your painting vertical!