if thats the nut that wasn't properly touqued/tightened ?, then i'd say you won't need a clutch holder to get it back apart, but you should use one to reassemble it.
or.....
redneck style:
rivet a steel clutch plate to a fiber clutch plate, insert into clutch basket, bike in gear, holding rear brake on will lock it up too
thats how the clutch transfers the power from the outer basket to the inner basket attached to the tranny, the fibers teeth lock to the outer basket, the steel plates teeth lock to the inner basket, friction between the 2 transfer the power, but when riveted together makes them locked together.
when in gear and brake applied locks everything up and will allow that nut to be removed.
they gotta stay alinged as they would be inside the clutch, then drill 3-4 holes around them and use pop rivets to hold them together.
best way would be to have a steel and a fiber in the basket, held out near the ohter edge by something ?
little pieces of wood, rubber ect.
then carefully drill the holes not allowing the bit to go thru too far thru and hit the basket.
a short doulbe ended pop rivet drill bit would be good.