This is going to look complicated, but it's actually easy once you do it once or twice. Not just for you, alap, but for anyone who hasn't shared because they didn't know how....
1. Click on the time the tweet was sent (e.g. 3h, 53m, etc.). That will open the individual tweet in a new window. Copy the URL.
2. Click on Post Reply to add to a thread, or New Topic to start a new thread.
3. On the top of the text window, click a button marked "tweet". Past the URL of the individual tweet in between the two bracketed words, so it looks like this:
['tweet]
https://twitter.com/TFroehlig/status/831693502522224640 [/tweet']
4. Add any text you'd like above or below the line.
5. You can view how it will look with the preview button, or submit the post with the submit button.