--Many moons ago Coles Power Models sold a widget that did just
this; not sure if they're still around or not but you might have a look.
Maybe ebay too.

--
"Steamboat Ed" Haas : Steel, Stainless, Titanium:
Hacking the Trailing Edge! : Guaranteed Uncertified Welding!
www.nmpproducts.com
---Decks a-wash in a sea of words---