I had planned always for a half-way point on the fixed/removable front armrest concept. Now that I know the inboard travel of the bottom of CZSA I can make the stick cover/access panel. Over the last few days:
I make up some foam/plastic/modelling clay/tape forms, and tape the surrounds. Fit the armrest inserts with some dobs of hot glue, and micro the foam. Still a bit short of BID, so make the covers from 4 x 4oz and peel ply.
The mechanics of peeling them off mostly delaminate the inserts so refit with urethane glue. The covers are a bit flexible, so patch over the travel of the CZSA bottom with 3 x UND tapes on the outside, with peel ply.
All seems to work fine now, and not as flexible. Fitted with sheet metal screws into previously prepared wood hard points.
Note on cure that I'll have to remove some material inboard, as I can't get 20.