William Bagwell wrote:
...
Have access to an old 6" jointer and think modifying the knives with a series
of flats leaving a row of cutting tips spaced approximately 1/2" apart *might*
just work. Cutting at least 12 grooves in one pass.

I like that idea. The 12-in-one-pass is an efficiency that you won't
get with anything else. Well, you could take a 12" planer & modify its
knives.

Looking for ideas that are better than just goobering up a set of jointer
knives with a hand held abrasive blade. ...

That sounds good to me, too. Clamp or bolt the knives together to be
sure of getting the "teeth" aligned, do a rough layout with Dykem (the
spacing and width will tend to vary a lot if you just wing it). I have
a holder for my angle grinder, so I'd use that & hold the knives in
hand, but vise-ing the knives & holding the grinder wouldn't be much
harder. I'd use a cut-off blade for better definition of the edges.

Sounds like fun.

Bob