Bikerumor reader Ricardo Wang just sent over this little hack.
After digging through his parts bin, he remembered a Yumeya carbon fiber XTR derailleur cage he’d purchased and never used. Turns out it’s a perfect fit for the Dura-Ace Di2 rear derailleur. While he says he doesn’t plan on using it, it’s a fairly cheap experiment compared to the full Ki2 kit from K-Edge, which he compares on his blog. Of course, you’d still need most of a Di2 group and K-Edge’s nifty machined shift pods.