I don't think that level of gaming the system is allowed. Let's say that the transoceanic legs (Pacific or Atlantic) have to be on a US carrier or code share through them.

I believe it WOULD be possible to do something like: take Ethiad from Bangalore to Abu Dhabi, and from there to London, spend a couple days in London, then take a US carrier back. But I was surprised at the high cost of transatlantic tickets. For example, flying Polaris from London to LAX nonstop was $10,000 by itself, more than 3x the cost of Polaris to Singapore over the pacific, despite being 5 hours shorter flight time. Must be a demand-based price. Premium economy on that leg is $3,400 so I could still get some time on an A380 if I flew back that way.