Here are the basic parts you will need.
A shimano or Suntour double cable stop
And a set of STI or ERGO stops.
This is the first modification grinding
Both side of the stop to fit into the new
STI or ERGO stop.
The stop now fits into the new adjustable stop.
Here we have a bad picture of the end being ground flat.
An easy one just center punched the end to help with the drilling.
You guessed it now it is drilled.
Here you can see we need to change the screw
that will hold it on to a longer one that will
go into the old stop and engage a nut.
Here is the modification that I did to the nut
just file two opposite sides a little and keep
test fitting it in from the back.
This is the bad picture of it all together.
Here it is again one side all done now the other side.