In article snipped-for-privacy@4ax.com, snipped-for-privacy@spaced.me.uk says... <snip>
Can you set it up as you want it, then drill new holes about 30mm from the end of the outer and add new bolts, suitably oriented, to stiffen the end. Perhaps with shims slipped in, either metal shims or those plastic shims that window fitters use. I expect they aren't very robust, but they are cheap. They go in 1mm steps.