Have the entire party zone into an instance, with the first player using their trinket to apply the first buff (ex: Versatility) to the party.2.
The first player can then zone out, while the rest of the party remains inside, and use one of the scrolls to change their trinket to provide a different buff (ex: use Canto Funebre dell'Evocanebbie
to change the trinket to Critical Strike).3.
The first player then zones back into the instance, and uses the trinket again, applying their second buff to the party, without overwriting or removing the first.4.
That player will repeat this two more times, until they have granted Versatility, Critical Strike, Haste, and Mastery to the party, following which they will remain inside the instance without zoning out anymore.5.
The second player will then go through the same process - using their trinket to apply a group wide stat buff, repeatedly zoning out to use a scroll and zoning back in to apply a different secondary stat buff, until every player in the party has two Versatility, Critical Strike, Haste, and Mastery buffs.6.
The third player will then take over, followed by the fourth, and then fifth - resulting in 5 versions of each secondary stat buff on each player, totaling 20 buffs on each member of the party.