hey, I did something like this for a client using the expand/collapse row feature. You basically setup your rows like this:
first row: toggle text button (you could call this 'index')
second row: thumbnail grid
third row: project index
Right click the project index row (make sure the project index isn't dragged all the way to edge as you can't right click) and choose 'collapse row' (you can now move the index all the way to grid edge) and then open the text box on the first row and highlight 'images' and choose the button in the top centre with the up and down arrows 'expand/collapse row' link. This opens a dialog box, in there you could change the replacement text to something like 'images' and then click 'row 2' and 'row 3' so they are selected and then save.
I found in my scenario that turning off the 'collapse other rows' and 'scroll to expanded row' to work best and importantly making the gutter 0% between rows 2 and 3 so when you toggle between them they appear at the same height if that makes sense!
Hope that helps!