Learnt the trick for that. That'll land in the next Welcome update. 
Currently undecided. 
From a technical point of view, these may make the searches more privacy invasive then visiting the page directly via HTTPS.
- Google/DuckDuckGo send queries using GET (exposed in the URL, ISPs/snoopers could read this)
- Startpage/lxquick use POST by default (nobody can see the query in the URL).
Startpage/lxquick does support GET queries too, as far as I can see, not POST. If privacy is the main concern, you may wish to re-consider whether you'd want us to add this.
If were to decide against adding it, there could be a modified version of the page that you could use locally in your browser. 