In the appSettings section of the web.config file for your SharePoint web application, you can add the following element:
<add key="SVGViewerPage" value=http://myAdobeSVGServer/ />
For RtWebParts, most likely the web.config will be in c:\Inetpub\wwwroot, however you should verify the proper path to the Sharepoint web application with IIS Manager. The "value" attribute for the "add" element is only part of the path that RtWebParts will use to retrieve the Adobe SVG Viewer, and it must end with a backslash. For the example above, the actual URL used would be http://myAdobeSVGServer/viewer/install/auto.
Note that this mechanism is not documented, tested or supported, but I believe it to work as desired.
Great! Thank you very much Paul. This saved a lot of time.