Well, here are the pictures of the cushioned mounting straps I found for the motorcycle crowd, but I guess anybody can use them.
They are simple and hold the tube really tight.

Here's a couple with the tube in the mount.


Here's one with the mount off, you can see the vinyl dipped portion on the strap, and the mounting holes for a single screw.


I didn't have a tach or speedo to mount this on.  Pretend the can is your speedo housing.  A singe hole in the side, and a bolt, nut, and lock washer, and you're done.  I'll get a shot of a friends tach with exactly this setup.