The Stretch in "Salvatore called a meeting" can be aquired without cheating. The game will force you through walls if you are persistant enough even without the speedup cheat activated.
The Bulletproof Trashmaster (featured in "Blow Fish") -OR- the above Stretch can be saved without cheating. This involves never entering more than one other vehicle at a time before revisits to your vehicle of choice, while the remainder of Portland's missions are completed back-to-back. Because most of the remaining missions require you to use a mission vehicle, it's probably not possible to do this with both of the special vehicles.
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