I'm seldom here these days, but your post caught my eye. Clansfolk, why would you want to fret a fiddle?
Many fiddlers, when they are starting out use a thin strip of electrical tape which they traditionally place at the E position the F sharp position and the G position on the D string, to use as a guide. Eventually we get to the point where we realize that we don't need the tape, so we gleefully remove it. I agree with the above posts that suggest that frets would hamper your ability to slide and to do many of the ornaments that are frequently a part of the fiddler's craft.
A mandolin is tuned the same way as a fiddle, so another fiddler's trick is to use a mandolin to perfect the fingering. The challenge with this is that you will have learned the song perfectly well, but you have to relearn it for the fiddle, while you are figuring out the bowing patterns.