Di2 onto retro steel frame.

[EddieJT]

I already have the Di2 stuff, that I cobbled together for a fraction of what eTap would cost.

 

[Gazelleer]

Re:

...but you'll ruin a classic frame in the process... unless you have something that already has fallen into the hands of the fixie/SS squad...

 

[EddieJT]

Must admit, I'm reluctant to drill the frame for that very reason; which is why I've now plumped for this: http://xshifter.com/

 

[Mercianbloke]

You could do it easily enough, the only difficult part would be getting the rear derailleur cable out of the chainstay. You won't have a hole for that so I'd advise taking the cable out the bottom of the BB shell and routing it where a normal cable would go to the back. Guiding the cables through is easy, they're only short and all meet at the BB.

 

[mattr]

Must admit, I'm reluctant to drill the frame for that very reason; which is why I've now plumped for this: http://xshifter.com/

Hmmmmm, zipties everywhere.

 

[Gazelleer]

Re:

How about these at the underside of the downtube and chainstay? Especially on a darker coloured frame you will hardly notice.