OiH is a Safari extension which, upon right-clicking a link, will offer the option of opening that link in the excellent Helium.
You can download the latest version right here. Double-click the downloaded
.safariextz file to install the extension.
See it in action
In theory, the extension can automatically be updated to the latest version as work goes on. I haven't tested it yet.
Open in Helium was created, and is maintained, by Brian Gilham.