I think, its not possible in Standard.
You can try with some development.
You can create 2 user statuses i.e., one is for normal & another one is for reservation creation. Give the authorization to change from 1st status to 2nd status only to some authorized people through Authorization group concept.
Keep "Never" as default option in PR / Reservation creation for your desired plant & order type combination.
Once you change the user status, while saving the order, check the current user status & change it to "From Release" at order level for all operations & materials.
