It took a while to find but I remembered reading several years ago about a shifter that does exactly what you describe. It's called a T&F Shifter. Here's a link:

http://www.hotrodscustomstuff.com/OLD_SITE/TFshifter.html

And here's another link with one happy customer, and a different phone number:

http://www.jalopyjournal.com/forum/showthread.php?t=427387

1960 GMC 1/2-Ton Pickup Truck
In the Gallery
Updates in the DITY Gallery
Now cruising in the Passing Lane