Hi Fred,

i just discovered a way to kind of / sort of do this, and I remembered this idea (wich i had already liked, as it should be readily available) so I'll share here, maybe this will help you.

You can design your block in such a way that an expand / collapse option is available where it is used.  It is not perfect, because you get to see a meaningless placeholder when expanding, but apart from that, it roughly does what you want.

1) make 2 nested If False's with the second one in the false branch of the first one (so true branches are only shown in SS, False branches are only shown in browser (pale blue dots)

2) decide what you want to show in SS in the collapsed state when using this block

[option 1] in the first true branch, you put something that will only be shown in SS, not in browser, (like an icon).  Downside is that expanded view in SS is not a perfect preview for browser, because that icon is still shown (red dot)

[option 2] before the first if, you put the first real element of your actual block and you leave the frist true branche empty.  Downside is that this first real element of your block might not be very representative, or might still be too large for your liking.  

3) In the false branche of your outer If False, you can put all (the remainder of) your real block content (yellow dots)

So far, this will only show a collapsed view wherever you use this block, as it will only show true branches in SS

And here comes the cool trick :

4) In the true branch of the inner If, you add a placeholder.  (green dot)

As far as I can tell, they had to allow an expand option on this, because the placeholder has to be available to put stuff in.  and the whole parent structure the placeholder is part of, gets also shown as a bonus.

So, in this picture, you could remove the icon (red) and move the first yellow container to the top of the block as an alternative.

Dorine