You don't, you leave it out. Now you can put a checkmark on doing your first mod
Seriously, myself included, most people enjoy the extra leg room w/o holder/manual there and remove the holder purposely. Then just toss manual pouch either in center compartment of rear parcel shelf, on floor behind one of seats or in spare tire cover in frunk.
Congrats on your new to you Boxster and be sure to join your local PCA region. It's cheap, many have fun events and most dealers offer discounts for parts to members.
Good luck & enjoy
