Halliday & Matthiessen (2014: 566):
The hypotactic extension of adverbial groups/prepositional phrases is essentially the same as that for nominal groups, with as well as, instead of, rather than, etc.:
In government as well as in commerce, obviously, power was being defined as wealth, the accumulation of economic resources [[[ by which to live more comfortably || and to command more authority]]] .
It was far better for a weapon used for retaliatory purposes to be under the sea rather than on land.
A very important development is the building of research stations on the farms instead of in neighbouring towns.
By the time the Great Central was built || the trains could manage the gradients much more easily || and the Great Central line usually went across the valleys ... instead of round them like the earlier railways || so the distances were shorter || and you got better views.