Use Proxy with preferably winhttp.winhttprequest.5.1?

[Cusem]

I use a proxy in my script to query Google US through a US based proxy server (SERP tracking; google.com/ncr or &hl=en&gl=us are supposedly not accurate).

I use HttpSetProxy(2, "proxyip:proxyport") and _InetGetSource($url)

_InetGetSource produces @error=13 often though which makes the script unstable.

I rather use $oHTTP = ObjCreate("winhttp.winhttprequest.5.1") to get the HTML source, however HttpSetProxy is disregarded.

I found topics about configuring a proxy by modifying registry keys, however I rather use another solution (not in favor due to rights / antivirus+antimalware).

What would be another good solution to get the HTML source of a Google.com query using a US based proxy?