With the new "popup form from other button" support in 5.19 this is now possible.
So what you'd have is a normal form (A), on the right table, with the "subset" of fields you want the user to see. Then create another procedure (B), a _memory form_, but which uses other fields from the same table.
Form A has a button, which calls Form (B) as a "popup". Because everything is session value based, form (B) is jsut setting session values, which should then be included when the SAVE button on form (A) is pressed.
I've not tried this layout yet myself, but it should work.
cheers
Bruce