Isn't it obvious?
1. Map out to position of timing mats and photographers. If the info is not available, check out the previous editions to see whether they are consistently in the same places.
2. position several bikes (use code locks) along the route past the timing mats/photo points and use them to ride the sidewalks/back streets between the checkpoints. It is imperative to run through all timing mats, but you are free to miss some photo points.
3. wear sport-casual clothes, someting like long shorts, cotton t-shirt. Wear your bib on a removable belt, so you are not too obvious to the bystanders. For good measure you can switch headwear (baseball cap, hat, bandana) or sunglasses on/of.
4. run like hell from the start to your first bike so that your first split is not too off. Run like hell from the last checkpoint to the finish.
Might shop around for the right marathon to pull this off, but perfect crime requires perfect circumstances.