It simply requires a guild to have a pool of members that: (1) all have the arc and (2) are committed to leveling up their arcs. There are numerous variations, but the basic gist is me and 5 of my guild mates contribute all of our FPs to each others Arcs. When Arc A levels, the 5 of us that contributed get rewards, that includes FPs. We then use those FPs to fund the leveling of the Arc B for a different player....and so on.
To use some examples:
1. Leveling an Arc to level 20 requires 1,242 FPs. The rewards for doing so are 440 total FPs, or 35% of the total.
2. A level 40 arc requires 2,035 FPs to level, and returns a total of 1025 FPs, or 50% of the total.
3. A level 60 arc requires 3,334 Fps to level, but the rewards are 1660 FPs, or roughly 50% of the total.
So, once you hit level 35 or so, half the FPs needed to level the next arc are created when you level the current one. Moreover, the FPs rewards noted above are pre-bonus. So, if everyone that contributed had a level 40 arc, they all get a 62% bump to their rewards, taking the 1,025 FPs up to 1660 FPs total, which is now 81% of the costs of leveling the next Arc (at level 40).
As an FYI, this process could be used for any GB, but because the Arc increases each players FP rewards, it dramatically accelerates the process.