The 2 for 1 isn't really random. If you have a ton of BP for a GB (200+ full sets). Select two BPs to trade and hit trade, track the BP position given . Do this again with the same two and again track it. Repeat with the same 2 until it rotates back to the given in step one. Repeat this for other pairs until you get the pattern. All would take about 500 BP sets.