Jim,
I recently had to replace the water temp gauge on my SPF. I had the same concern, A small hole in the fire wall and you have to get the large fitting through.
There is enough room to get the fitting through and an additional water or
oil temp line. First off, when you remove the rubber grommet you will see a groove that extends off the the main hole to slide one of the temp line into. This is there to make enough room for the fitting. In my case I had the speed cable going through the same hole so I had to remove the speedometer cable first. It's not as difficult you it first appears.
As Doug mentioned, the gauge may be under warranty.
Dan