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Otherwise Google led me to this Penn Elcom Under Desk Laptop Drawer, Lockable, for 550mm/20 Inch Laptops - Premium Sliding Security Drawers https://www.amazon.co.uk/dp/B01M9JN63B/ref=cm_sw_r_other_apa_i_n2O0Eb66PRP8G
That can't work as the frame would get in the way.
But it did lead me to https://www.amazon.co.uk/Emuca-bearing-underdesk-platform-adjustment/dp/B076CSNNG8 and the mounting brackets (green in diagram) can attach without being fouled by the frame and then I can use a thin piece of plywood (red outline) as the tray.
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Photos would be good.
But my first thought is mounting some sort of set of U-brackets to give you the equivalent of screwing into the frame.
Or make black paracord hoops.
Or even better use this as an excuse to buy a decent helicoil set.
Otherwise Google led me to this Penn Elcom Under Desk Laptop Drawer, Lockable, for 550mm/20 Inch Laptops - Premium Sliding Security Drawers https://www.amazon.co.uk/dp/B01M9JN63B/ref=cm_sw_r_other_apa_i_n2O0Eb66PRP8G
Which would have the advantage that you can access it if needed.