Thanks everyone for the feedback.

Here's an updated flights URL that includes all 3 alliances:
https://www.google.ca/flights/#searc...,SKYTEAM,AS,WS

The only drawbacks with this approach is that it may exclude non-alliance members where milage running makes sense (I've added WS and AS since they are well known examples of this). Would love to hear whether there are other non-alliance airlines that should be added to the list.

I'll also be looking into finding a way to get flights to exclude basic economy fares, since other than perhaps AA they are worthless for pure MRs.

Safe Travels,

James