Yes I agree the combination of yoga sukshama vyayama with mountain pose as suggested by you. We should also follow the most important sutra of Patanjali Yoga Sutras defining asana as Asanam Sthiram Sukham which means that asana is that wherein we are stable and comfortable physically as well as mentally. So, in case we are not able to maintain the posture completely, never mind. One should do it within his capacity and wherein he feels comfortable, otherwise, it should not serve the definition of asana and hence, cannot get the full benefits of asana meant for. So, one should not care of flexibility just be persistent with small small steps and after a long period of time, he will be able to establish in asana enough to the perfection.