Have you looked at cable stops on your frame?
Hydraulic or mechanical brakes?
If the frame was designed for Di2, it is possible it was designed for different wire routing than it would have had with mechanical derailleurs.
There may be ways around it, for example sourcing vintage clamps, or using full length cable housing.
tiCycles in Portland likely could add/modify cable stops, as well as potentially your bike's manufacturer. However, the cost of modifying your frame could exceed the cost difference in groupsets.