items of different heights or dynamic heights

Without pre-rendering and measuring, is there support for items with heights which are not know before hand? If not, I tried a work-around where all items are the same height, but **expandable**. But is this supported since the height has to change dynamically?
I tried the following for a expandable list item:

```
{{#ember-collection
items=model
cell-layout=(mixed-grid-layout dimensions) as |item index|
}}
```

Then, in Ember, i changed to height of one item via
`this.get('dimensions').replace(index,1,[{width:1000, height:2000}]);`
But ember-collection doesnt seem to observe the dimensions array. How can I support either of the above cases?