Disclaimer first - be careful with sharp objects, always be thinking where your fingers and other necessary extremities are!
More modern kits don't require quite as much cutting, but the Berserker kit is a few years (or rather more) old at this point.
I would use an X-acto knife (or similar), cutting just above the end of the glove bit and then filing down the last mill with a small file.
Protect the surface underneath with a cutting mat.
Another way would be a fine razor saw.