2:13 PM, Wednesday August 5th 2020
Hi, sorry to hear of your situation. I think you really need to cut yourself some slack on this issue as it shouldn't interfere with your enjoyment of drawing. I would suggest two possible options one involves pursuing drawabox and one not.
Drawabox option.
De-emphasise the shoulder thing. Yes ideally that is what we should be doing but if you can't, you can't. Your situation is much different to someone that just isn't putting in the effort. Focus on just doing your best to achieve the results in those lessons you can. Much of the construction approach applies regardless of whether it is one fluid line or ellipse or not. Try to achieve a similar result even if not strictly in the manner specified. Maybe work on a smaller scale, microdrawabox :-) or something like that.
Non-Drawabox option.
Look for other courses or options. You will find that many artists don't particularly follow the from the shoulder approach to produce their work ( most of those on iPads for a start ). Often the limitations that we have actually encourage us to find solutions that create highly unique and brilliant works in new styles. Matisse made paper collages when his health was unwell and couldn't paint.
Hate to thinking of you sweating over this fairly technical aspect when you could perhaps be really enjoying some other style, method or technique.