Others have drilled and tapped the crankarms to mount a 3rd chainring , including Campagnolo them selves..

I have a Gippiemme triple (will sell) they made theirs so the 3rd ring an 86bcd
went into the back side of the crank spider, made thicker so hole didn't go through.

I have it set up as a 36 - 52 + a Campag 222. chain guard disc as the outside ring . looks great, too ..