Some thoughts- Torque applied to each joint is case specific. I know there are charts and all, but they don't account for YOUR situation such as screwing a fab to a chassis(or your aluminum screw).
If the customer sets a spec then use it. (But it probably won't satisfy his requirements) So have an alternative value as a backup.
I like Dave's second reference. Do your homework, find the point of joint failure, and set a value of 50 or 60% of that.
It means you must have a torque control program. That is, how do you set your tools, how do you check your tools ...
I worked at a contract shop, #1 defect with one customer was 'loose fasteners'. They did not have specs, so I developed my own (some brass screws) and gave them a shot at disproving them. Put a torque control program in place. (you cann't believe the numbers on the side of many tools) After a little customer education (can't check tightness of a joint with the same value that made the joint due to 'joint relaxation') the problem went away. My point - IT CAN BE DONE!
Go for it.