Start at the furthest most point near the top (that is still straight and attached). From there down remove all screws and check the framework to see if the screws will still go back in and fasten tight. (If not-then add wood filler to the screw holes and allow a minimum of 24 hours to harden)
---After the wood is solid enough to accept screws again, then apply some butyl tape (strip caulk) to the aluminum trip, and start forming the trim to the walls (by using a rubber mallot), and applying screws as you form down.
If you take your time-work/form slow, and attach screws tight (but not so tight they "strip out") you can perform this task, and nobody will ever know.