Adding shims with stock secondary spring question

Recently added a set of 28" mega mayhems to my grizz and needless to say they sucked out a lot of power. Need to do something to combat this but can’t go for a machined clutch at the moment so I was thinking of adding shims, probably 1.0mm, but was wondering if it was completely necessary to change out the secondary spring for a stiffer one.

Any insight would be appreciated, Cody